• Prologue | The Invisible “Axis” That Changes One’s Life
• Chapter 1 | The Center of Gravity, the Arch, and the Human Body’s Innate Balance Mechanism
• Chapter 2 | Upright Bipedalism and the Freedom of Foot Contact
• Chapter 3 | The Chemical Reaction Between External Force and Internal Force Creates Movement
• Chapter 4 | The Psychology of Consistency and the Recovery of Physical Freedom
• Chapter 5 | Human Essence and the Return to the Neutral Self
• Chapter 6 | The Awakening of Primitive Reflexes and Movement as Self-Expression
• Chapter 7 | Pelvic Angle and the Three Postural Types: The Way of the Balanced Body
• Chapter 8 | Nanba-like Movement and the Reconstruction of the Body Through ippon blade
• Chapter 9 | The Fundamental Principles of Movement and the Redefinition of “Kata” in the Modern Age
• Chapter 10 | The Wisdom of Human Balance Taught by Play and Fluctuation
• Final Chapter | The Path Called ippon blade: Reclaiming Yourself Within Movement
• Afterword | Everything I Put Into “The Single Tooth”
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An Essay on ippon blade®︎ | Chapter 1: The Center of Gravity, the Arch, and the Human Body’s Innate Balance Mechanism
How do human beings stand, walk, and run?
These everyday actions may seem completely ordinary at first glance, but behind them lies the invisible movement of the center of gravity and the delicate support structure created by the arch of the foot. Even without conscious awareness, our bodies are constantly activating a system that prevents us from falling.
First, the center of gravity refers to the point at which an object’s balance is maintained. In the case of a seesaw, it is the central pivot point. In the case of a pendulum, it is the supporting post from which it hangs. In the human body, the center of gravity is the “center of weight” of each part of the body as a whole.
If we divide the body broadly into three parts, they are the pelvis, including both legs, the torso, including both arms, and the head. The center of gravity of each exists below the navel, at the solar plexus, and between the eyebrows. The line connecting these three centers of gravity in a straight line is called the “line of gravity” or the “axis of gravity.”
The point where this axis of gravity meets the ground is called the “gravity drop point.” When the human body is viewed from the side, the axis of gravity descends through the temple, the shoulder, the greater trochanter at the root of the thigh, and the tarsal bones before reaching the ground.
The tarsal bones are the group of bones that form the uppermost part of the foot and constitute the “ceiling” of the plantar arch. They are a crucial structure. These tarsal bones become the central point for supporting the body’s center of gravity.
Whether the center of gravity is stable or not depends on the “base of support” while we are standing. This refers to the area of contact needed for an object to maintain balance. In a four-legged animal, it is the area enclosed by the four limbs. In bipedal locomotion, it is the area enclosed by both feet. In standing on one leg, it is the area of one foot.
The center of this base of support is called the “center of pressure.” The more closely the gravity drop point and the center of pressure coincide, the more naturally and upright the body can stand. Conversely, when the center of gravity moves greatly outside the base of support, the body tilts and eventually falls.
However, even if the center of gravity of each body part moves, the body will not fall as long as the overall axis of gravity remains within the base of support. This is the reason human beings can move even in unstable situations.
The foot forms an arch through three points: the ball of the big toe, the ball of the little toe, and the heel. This arch extends both longitudinally and transversely, and it is an essential structure that supports our body weight as a whole.
The center of this three-point arch is also the tarsal bones. By aligning the axis of gravity seen from the side of the body with these tarsal bones, the center of gravity is distributed evenly across the entire three-point arch, and the arch’s original function begins to operate.
There are two especially important mechanisms in the functioning of the arch. One is called the “truss mechanism,” which acts to lift the body against gravity. The other is called the “windlass mechanism,” which serves as an adjusting mechanism that continually keeps the center of gravity within the base of support.
In the tarsal region are small joints such as the Chopart joint and the Lisfranc joint, and as these move subtly, the balance of load distribution in the front, back, left, and right is constantly adjusted.
When the axis of gravity coincides with the center of the three-point arch, the pelvis neither freezes in anterior tilt nor collapses in posterior tilt. Instead, a “neutral pelvic position” is created, one that can move flexibly in all directions while naturally returning to the center.
To maintain this neutral state, our bodies are equipped with a homeostatic maintenance function called a “negative feedback loop,” that is, “homeostasis.”
For example, the balance between the sympathetic and parasympathetic nervous systems, the regulation of blood pressure and blood sugar, and the “stretch reflex,” in which a muscle contracts when it is stretched, are all part of this homeostatic function. Both the truss mechanism and the windlass mechanism are based on this principle.
When the center of gravity tilts to one side, a force opposite to that direction automatically comes into play to restore posture. Because of this, even unconsciously, we are able to avoid extreme bias and regulate the overall balance of the body.
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The greater the instability in the center of gravity becomes, the greater the rebound and energy required to bring it back. To prevent falling, an unconscious force presses against the ground, and this in turn creates unnecessary tension in the body.
To minimize such instability, the “inner muscles” that support the axis of gravity from its root play an important role. Among them, the psoas major is especially important. The psoas major connects the center of gravity of the pelvis with that of the torso, functioning like a bridge between the lower and upper body.
This psoas major does not always work in a fixed direction. By repeatedly lengthening and shortening, alternating between tension and relaxation, it continues to preserve the balance of the entire body with suppleness. Anterior and posterior pelvic tilt, the expansion and contraction of the rib cage, lifting the leg out of the hip through the knee, and even centripetal “pulling out” and centrifugal “extension” are all among the central functions governed by the psoas major.
In the first place, the act of “walking” itself is nothing other than the “movement of the center of gravity” through a continuous sequence of single-leg stance. Movement becomes possible by continuing to place the body’s axis of gravity onto the base of support of the leg that has stepped forward.
Traditional Japanese sliding-foot walking is an extremely refined way of moving that realizes this transfer of the center of gravity with minimal force. Rather than consciously using muscles strongly, it maintains balance and, within natural fluctuation, stabilizes the axis of gravity through the two lateral axes while proceeding smoothly.
By contrast, in modern “model walking” or “sport walking,” the left-right axes are moved more largely, and the entire body is linked together through the use of the stretch reflex of the muscles. In that sense, it becomes a more wild and dynamic way of walking.
This is not a question of which is correct. What is desirable is a form of physicality that understands the principles of both and can naturally use each one according to the situation and purpose.
The same applies to foot strike. People often debate which is correct among “forefoot,” “heel contact,” and “midfoot,” but the issue is no different. What matters is whether, regardless of which part touches down first, the center of gravity is properly placed and the function of the arch is being utilized.
And for that, it is first necessary to align the axis of gravity with the “tarsal region = the center of the three-point arch.”
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Chapter 1, Second Half | What Does It Mean to Set the Pelvis Upright?
Once the axis of gravity has been aligned with the tarsal region, the next important thing is to “set the pelvis upright.”
To set the pelvis upright is equivalent to setting the ischial bones upright. The ischial bones are the bones on the left and right sides of the buttocks that touch the seat surface when you are sitting. When these ischial bones are vertically upright in relation to the floor, the pelvis naturally stands straight, and the upper body can be stacked on top of it without strain.
When sitting in a chair, the ischial bones themselves become the fulcrum supporting the center of gravity. Even when standing, by maintaining the awareness of directing the ischial bones vertically toward the ground, it becomes possible to keep the pelvis upright. At this time, however, care must be taken, because if the knees bend, the angle of the pelvis will collapse.
The pelvis is supported by two fulcrums, the left and right ischial bones, that is, two axes. Only when the balance between them is organized does the whole body naturally begin to move with coherence, like a single cylinder. Furthermore, through the whole body there runs a “single axis” centered on the sacrum, and by moving the two axes, the left and right ischial bones, relative to this single axis, it becomes possible to manipulate the body in a way that combines both flexibility and stability.
For example, four-legged animals have movement patterns such as “lateral sequence,” in which the foreleg and hind leg on the same side move together, and “diagonal sequence,” in which the diagonal limbs move together. If we translate this into the bipedal human body, the lateral sequence corresponds to a two-axis use of the body, and the diagonal sequence corresponds to a one-axis use of the body.
In the human case, because the length of the arms and legs differs, a complete lateral sequence may appear unnatural. Even so, in terms of upper-body use, it remains an extension of the way the forelimbs were used in our quadrupedal past. In other words, the way one runs and walks is something that can freely shift between axes according to one’s purpose and situation.
The “Nanba walk,” known as the walking style of Japanese people up until the Edo period, is often explained as “a way of walking in which the arm and leg on the same side move forward together.” This theory is thought to have arisen from modern people observing the walking figures depicted in ukiyo-e prints and interpreting them from those frozen moments of composition.
In reality, it is more physically reasonable to think that the arms and legs did not always move together, but that people walked while naturally switching between a single axis and two axes. In other words, “Nanba” was one bodily technique that emerged naturally in the course of organizing the body and seeking efficient movement, and if one tries to reproduce it forcibly, it becomes unnatural.
One reason modern people tend to forget this “natural movement” is the loss of sensitivity toward the “axes of the body.”
The human body contains as many centers of gravity as there are supporting bones and joints, and as many “axes” as there are lines connecting them. How delicately and how deeply one can access one’s own internal bodily sensations is the key to controlling those axes freely and realizing effortless movement.
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Chapter 2 | Upright Bipedalism and the Freedom of Foot Contact
The ways modern humans walk and run are remarkably diverse. This is deeply related to the fact that we are vertebrates that have undergone the peculiar evolution of upright bipedal locomotion.
Animals each possess skeletal structures adapted to their environments, and they employ limited patterns of foot contact. They may hop, crawl, climb, or creep, and although there are variations in behavior, the way they make contact with the ground is almost fixed for each species.
Human beings alone are different.
Humans are designed to make contact from the toes, from the heel, and even from the middle of the sole. This is the result of upright bipedal locomotion, which created “choices” in the act of contact.
For example, there is contact along the line connecting the ball of the big toe and the ball of the little toe, that is, forefoot. Or there is heel contact, entering from the heel. Or midfoot, entering from the tarsal region, the center of the three-point arch. It is not that one of these is correct. Each exists for a situation to which it is suited.
When running down stairs, when carrying a heavy load, when leaping up, or when wanting to walk quietly, in each of these situations the body naturally selects the most efficient contact method. Human beings are the only species capable of “using them selectively.”
This flexibility, that “there is not only one correct answer,” is the greatest strength of the human being. More essential than “how to make contact” is the question of “how to move the center of gravity.”
According to the inclination of the axis of gravity, the direction of bodily motion, the vector, changes naturally. If the center of gravity inclines forward, one accelerates. If it inclines backward, one decelerates. If it remains upright, one is in stillness or neutrality. Acceleration, braking, and neutral can all be controlled solely by the tilt of the axis of gravity.
Conversely, a form that is only “shape” without the center of gravity will not move forward, no matter how much muscular strength it has. When the pelvis has disengaged, in what is called swayback or leaning away from motion, speed does not increase, unnecessary tension arises, and movement becomes heavy.
Upright posture lies between anterior tilt and posterior tilt. It is the posture in which the axis of gravity and the central axis of the body are aligned. In that state, the downward force of gravity and the upward ground reaction force match one another, and the internal and external forces acting on the body are balanced.
And when even the slightest inclination is added to that balanced axis, the body naturally begins to move forward.
What allows one to physically experience that subtle balance is the single-tooth geta called ippon blade. At first glance, its contact surface appears to be extremely small and restricted. In reality, however, by placing the axis precisely onto the tarsal region, it allows one to gain the freedom to move the center of gravity in every direction, front, back, left, and right.
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Chapter 3 | The Chemical Reaction Between External Force and Internal Force Creates Movement
Human movement is formed through the interaction between “external force” applied from outside and “internal force” generated within the body. It is through the combination of these that motion occurs, direction is determined, and propulsion is produced.
External force refers to forces applied from outside the body, such as gravity, ground reaction force, and inertial force. For example, gravity is always acting from above to below. In response to that, the ground returns an upward ground reaction force. These two always exist as a pair. In addition, the inertial force generated when the body tilts as if falling forward is also one type of external force.
Internal force, on the other hand, refers to the interactions that exist inside the human body. The coordination among muscles, tendons, and the skeletal system, the autonomic nervous system, breathing, hormones, and even invisible physiological reactions are all part of internal force. For example, when the arch of the foot sinks slightly on contact and then rebounds into propulsion, the “stretch reflex” at work there is a typical expression of internal force.
Also, in the act of running, when the psoas major lifts one leg, a centripetal force that draws inward is generated, while at the same time a centrifugal force that extends outward is generated in the opposite leg as it lengthens. In this way, the internal reactions and chain responses within the body may truly be described as a precise “natural structure.”
Furthermore, environmental changes such as temperature, humidity, wind, and the slope of the ground are also included among external forces. Breathing, posture, and the autonomic nervous system respond to them, and internal force changes as well.
Movement is the state in which these external and internal forces are constantly undergoing a chemical reaction. It is not about moving in opposition to gravity, but about accepting gravity and responding to it. When receiving force from outside, what kind of response can the body return from within? There, movement that is “naturally in harmony” emerges.
Put differently, movement may also be called “an intelligent response to the laws of nature.”
When viewed from this perspective, even the distinction between where the outside ends and the inside begins is only relative. One way of seeing it is that “everything other than oneself is external.” Another way is to regard “oneself, others, and the natural world as all being inside the same universe.”
What matters is that depending on the perspective from which one perceives the world, the way one moves, the way one uses force, and one’s very way of being all change.
To switch perspectives according to the situation. At times to narrow focus, at times to overlook the whole. Sometimes what is needed is even a sensation like softening the contours and perceiving things through half-closed eyes.
In other words, “not fixing things into rigid conclusions” is the first step toward free movement.
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Chapter 4 | The Psychology of Consistency and the Recovery of Physical Freedom
We human beings possess a mental tendency to want to remain consistent with what we have decided for ourselves. In psychology, this is called the “law of consistency.”
The method one has chosen, the values one has believed in, the skills one has acquired. By maintaining these, one feels that one’s identity and the stability of mind and body are preserved. This psychology of consistency can be a tremendous force in building habits, and it also becomes a source that supports continuity.
However, if it becomes too strong, it can instead cause us to lose flexibility and become closed to change and evolution.
One begins to regard any methodology outside one’s familiar framework as “wrong” or as an “enemy,” and reacts negatively toward it. Such phenomena occur daily, even on social media. It is an unconscious function that tries to justify one’s own consistency by denying others.
This psychology of consistency also has a major influence on the way the body is used.
For those who grew up in sneakers and have exercised in sneakers, the idea that “exercise = sneakers” becomes completely natural. As a result, options such as barefoot, geta, or straw sandals come to appear as nothing more than eccentric alternatives.
But that simply means that the way the body moves has been strongly restricted by the “mold” of sneakers. The body has been optimized for sneakers as a particular framework, down to the way muscles are used, the range of motion of joints, the way the foot meets the ground, and even the speed of reaction in movement.
On the other hand, if one leans too much toward classical Japanese movement forms such as sliding-foot motion or Nanba, they too cease to fit modern sports, fashion, and culture.
Likewise, people who have only cultivated soft, lengthening-based body techniques tend to become poor at movements such as jumping and acceleration.
Similarly, people whose training is centered on building muscle tend to become poor at opposite qualities such as relaxation and endurance.
In other words, if one continues conscious effort too much in only one direction, the body becomes “locked” into that particular mold, and other possibilities begin to close off.
Originally, all human beings share a set of “basic movements.” These are the minimal movement patterns necessary for living, not bound by implements or culture. Yet in modern life, even these fundamentals are gradually being lost.
Overly biased training, instruction bound by fixed ideas, numerical evaluation, and efficiency-first thinking. These are causing us to forget our “originally free physical operation.”
That is why what is needed now is not the denial of “kata,” but the recovery of a sensibility that can discern the form that is truly natural and unforced for oneself, and use it freely according to the environment.
If I am to hold consistency anywhere, I do not want it to be in a “methodology of physical operation,” but in a “neutral way of being.”
If one’s axis of gravity is organized, one can naturally adapt to any situation. I believe that state is “true freedom,” and the ideal form of human movement.
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Chapter 5 | Human Essence and the Return to the Neutral Self
What are we human beings, really?
This question has been discussed in philosophy, religion, science, art, and many other fields. But from the viewpoint of the body, perhaps a human being may be understood as “a being capable of changing oneself according to the environment,” and “a being that relates to the world through sensation and movement.”
Essentially, before being human, we are animals, living organisms, and life energy itself.
Life is that which transforms curiosity toward the unknown into energy, adapts itself to the environment, and evolves. In that process, it discovers a new self and continues changing endlessly. That flexibility and suppleness are our essence.
When people ask, “Who am I?” or “What is my essence?” many try to find an answer. But the truth is that the essence of the self is that it can become anything and return at any time.
Because it is “nothing in particular,” it can become anything.
Because it can “always return,” it can go anywhere.
That water-like, neutral, and free way of being is the original power human beings possess.
When a person loses this “neutral way of being,” they become tossed about by the environment, dependent on the evaluations of others, and both thought and body gradually harden. And the rigid insistence that “it has to be this way” stops not only oneself, but also others and society as a whole, from changing and growing.
What matters is not competing over which methodology is correct.
What matters is being able to return to one’s natural self, one’s neutral state. And it is to have a body that can, in any situation, move the center of gravity without strain, organize its axis, and express its power appropriately.
ippon blade is a means of re-experiencing that feeling of returning to the origin.
Rather than forcibly suppressing the natural force called gravity, one uses it correctly. Then movement is naturally drawn out from within oneself. It is never a matter of “making the body move by force,” but of cultivating “a body that wants to move.”
When we are released from fixed ideas and assumptions, the mind and body recover neutrality.
That neutral sensation is the “original form” and the “original way of being” of the living creature called oneself.
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Chapter 6 | The Awakening of Primitive Reflexes and Movement as Self-Expression
The human body possesses an inborn function called “primitive reflexes.”
These are the body’s automatic regulatory functions that respond instantly to stimuli, not through language or thought.
For example, when a baby touches something and the fingers naturally curl around it.
Or when we are about to fall and our hands or feet come out unconsciously.
All of these are manifestations of the body’s original reflexive wisdom.
Yet in modern society, there are not a few people who grow up with these primitive reflexes dormant, or without them functioning fully. That is because conscious control in daily life is emphasized too strongly: “Let’s create correct posture,” “Let’s walk beautifully,” “Let’s be aware of the muscles.”
Originally, posture is not something to be “made.”
It is something the body senses and organizes unconsciously.
If it wavers, it returns.
If it expands, it contracts.
If it fills, it recedes.
If it opens, it closes.
Through this repetition of natural balancing, the body continually maintains a middle way and keeps moving within harmony.
ippon blade gently awakens these primitive reflexes.
By moving within the restriction of single-tooth geta, the body unconsciously begins to search for “how not to fall.” In the course of that exploration, deep muscles that are not ordinarily used begin to function, the skeletal structures start to coordinate naturally, and the sensations of the soles and pelvis return in fine detail.
And the potential that had until then been used only to unconsciously correct unstable posture becomes available, once the axis is recovered, for “self-expression” and “performance.”
In other words, to organize the axis of gravity is not only to activate power for “defense” or “correction,” but also to freely release power for “creation” and “expression.”
There is no need to force power in order to move forward.
If one stands in neutrality and aligns gravity with the axis, the body will naturally be guided in the direction it wants to move.
Try standing while wearing ippon blade.
At that moment, your body will surely remember.
It will remember that forgotten sensation of “wanting to move.”
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Chapter 7 | Pelvic Angle and the Three Postural Types: The Way of the Balanced Body
Posture is not merely a way of standing.
It is the very “way of being” in which each part of the body relates to the others and maintains a particular balance.
What is especially important is the angle of the pelvis. The pelvis is positioned at the center of the body and serves as the relay point connecting the upper and lower body. Depending on this angle, major differences arise in the way muscles are used, in the state of the breath, and even in the functioning of the nervous system.
Broadly speaking, posture can be classified into the following three types.
1.Anterior Pelvic Tilt Type
In this type, the extensor muscle groups of the back are dominant, and centrifugal, outward-extending movement becomes the main pattern. In breathing, inhalation is strong, and this type is suited to aerobic exercise. The posture tends toward swayback and is suited to movement with speed and a sense of openness.
2.Posterior Pelvic Tilt Type
Here, the flexor muscle groups on the abdominal side are dominant, and centripetal, inward-drawing movement becomes central. Exhalation is deep, concentration in an anaerobic mode is strong, and this type is suited to introspective movement and held postures. It tends toward a rounded back, and its characteristic is a way of using the body that stores force inward.
3.Upright Pelvis = Balanced Body
This is a posture that does not lean toward either anterior or posterior tilt, and instead makes balanced use of the intermediary musculature between centrifugal and centripetal action, extensors and flexors, superficial and deep muscles, and slow-twitch and fast-twitch fibers. It is a way of being that can freely switch between inhalation and exhalation, tension and relaxation, force and release, and possesses “the power to return to center while still swaying.”
This balanced body is precisely the “state of axis” that ippon blade seeks.
When many people hear the phrase “set the pelvis upright,” they try to move the pelvis consciously. But if they do so, excessive force enters the large muscle groups of the lower back and abdomen, and the movement becomes unnatural instead.
The correct way to set the pelvis upright is to create a condition in which the pelvis rises into place as a result of “naturally aligning the axis of gravity with the center of the three-point arch of the sole.” If one imagines lengthening the hara vertically, the spine will naturally organize itself, and the axis will rise straight upward.
From there, simply by shifting the foot’s center of pressure little by little toward the toes or the heel, the inner muscles, beginning with the psoas major, take the lead and the angle of the pelvis is adjusted naturally. There is no need to forcefully arch or round the lower back.
In this way, by finely sensing the balance of axis and center of gravity and continually maintaining the most optimal position for oneself, the body begins to move not as a “shape,” but as a “flow.”
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Chapter 8 | Nanba-like Movement and the Reconstruction of the Body Through ippon blade
The Japanese body carries within it ways of moving that are uniquely Japanese.
One representative example is the bodily operation known as “Nanba.”
Nanba is often described, in contrast to modern walking, as a movement in which the arm and leg on the same side move forward together. In reality, however, it is a far more complex bodily technique involving delicate balance control.
In Nanba-like movement, there is an impression that the axis of gravity is always kept within oneself, and that movement is completed inside the body without unnecessarily crossing the left and right axes. This is highly suited to the Japanese form of physicality, which excels in centripetal movement and houses power within stillness.
In fact, Japanese people tend to have well-developed flexor groups and are good at centripetal movements that draw inward. In addition, they tend to have many slow-twitch fibers and thus excel in endurance and aerobic movement. In other words, the Japanese body has a structure especially compatible with “Nanba-like movement.”
ippon blade can be called a “means of reconstructing form” for reviving this Nanba-like physicality in the modern age.
Though its contact surface appears extremely limited, its very structure is what aligns the central axis of the body with the center of the arch and awakens the coordination of the whole body.
In fact, when wearing ippon blade, because the tooth of the geta is positioned beneath the center of the three-point arch of the sole, namely the tarsal region, the body unconsciously tries to grasp the center of balance. At that time, whether it tilts front, back, left, or right, the whole body automatically works to correct that deviation.
This is precisely the experience of “recovering the axis.”
And once the body has recovered the axis, it no longer fears instability. That is because no matter how much it sways, it remembers the power to return.
When in this state, the movement of the center of gravity ceases to be “something moved through applied force,” and changes into “something naturally carried.”
The true essence of Nanba-like movement lies precisely in this “feeling of being naturally carried.”
In other words, it is not “to move,” but “to find oneself already moving.”
Not to control it, but to receive it.
That is why it is quiet, beautiful, and powerful.
And this sensation can be applied to any action: running, jumping, throwing, dancing.
The bodily operation cultivated through ippon blade becomes the foundation of all movement, regardless of form of expression or cultural background.
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Chapter 9 | The Fundamental Principles of Movement and the Redefinition of “Kata” in the Modern Age
When we hear the word “kata,” in many cases we imagine some sort of “fixed form” or “traditional movement.” But originally, kata is the “extraction of natural law” through the systematization of the essence of movement. It is not mere imitation or mechanical reproduction according to a pattern.
Kata is a “structure” devised so that one may move along the flow of kinetic energy without straining the structure of the body. By following it, anyone can move naturally, effortlessly, and without unnecessary force.
I have not deeply studied the traditional “kata” of what are commonly called martial arts, dance, or sports. However, through my life experience, my bodily sensations, and the innumerable trials and errors through which I encountered realizations about movement, I have been confronted again and again by the question: “What is a truly natural and unforced form for my own body?”
The conclusion I arrived at is that “not fitting into a kata = freedom” is not true.
Freedom in movement is something obtained only by following the principles and laws of motion.
If one ignores those principles and moves however one pleases, forces will eventually oppose one another, the axis will become disordered, and the energy of mind and body will be wasted.
That is precisely why what is needed is “the redefinition of kata in the modern age.”
In this era overflowing with information and crowded with methods, we must discern which kata to choose and which structures to follow. No matter how traditional and beautiful a kata may appear, if it does not suit one’s physical structure, it will produce distortion and imbalance.
Furthermore, in trying to force oneself into a form that is unnatural merely in order to gain social status or evaluation, there is even the danger that the autonomic nervous system will become disturbed and both mind and body will break down.
I myself, in the past, had the experience of upsetting the balance of my mind and body because I was so anxious to become “someone” that I tried to fit myself into forms that society regarded as correct.
But it was precisely because I had that experience that I was able to encounter “the kata of nature.”
That was the process of running barefoot, encountering single-tooth geta, and recovering the sensation of moving in accordance with natural law.
In the natural world, there is not a single useless thing.
ippon blade as well is designed in accordance with harmonizing laws of nature such as the Fibonacci golden ratio and the Yamato ratio.
It has a structure that guides the human body, without imposing strain, in the direction in which it naturally wants to move.
In other words, ippon blade is something that allows the body to remember “the kata of nature,” and rather than opposing existing forms, it leads toward a “redefinition” of kata itself.
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Chapter 10 | The Wisdom of Human Balance Taught by Play and Fluctuation
We tend to seek perfection.
Straight, unwavering, strong, beautiful.
And yet in the natural world, nothing exists that is “completely motionless.”
Everything exists within fluctuation.
Wind, water, light, life, all of them continue changing ceaselessly while accompanied by fine vibration.
The human body is no exception.
Even when standing, walking, running, or appearing to be still, it is in fact always swaying slightly.
To allow this “sway.”
To know the range of this “play.”
That is the key to cultivating a true sense of balance.
“Play” refers to the range of motion within which freedom can be expressed inside a limited space.
For example, the range through which a pendulum can swing from side to side, the safe range within which a joint can move, or even a sport in which one moves freely within rules, are all forms of “play.”
When one stands on ippon blade, this very “play” rises to the surface as sensation.
In response to even the slightest displacement of the center of gravity, the body immediately tries to return a response. Within that continuity, the body learns fluctuation, searches for the middle, and then sways again.
A body cultivated in this way neither hardens nor runs wild. It continues at all times to search for the optimal balance of “this moment, here and now.”
It is like water: fluid, not bound to form, and capable of adapting to any place.
By recovering this “range of play,” I was finally able to feel that life itself is also “play.”
If I push too hard, pain comes.
If I become too lazy, balance also collapses.
Without swaying too much and without hardening too much, I drift gently in between and return to my own axis.
This, I believe, is “human movement,” and also “a human way of living.”
ippon blade offers a “fulcrum” for that.
Even when mind and body fall into excessive tension, if one remembers the axis, one can return.
Even in unstable circumstances, if one stands in accordance with gravity, stability wells up from within.
No strain, no bracing, no force is necessary. One only needs to ride the axis.
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ippon blade is not merely single-tooth geta.
It is one “path” through which modern people can recover the “original physicality” they have forgotten.
How will one live with this body?
How will one play on this Earth?
It helps one remember the answer from the ground beneath one’s feet.
Yes, the “path” has already begun beneath your feet.
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Final Chapter | The Path Called ippon blade: Reclaiming Yourself Within Movement
We live surrounded by far too many “methods” and “correct answers.”
They are knowledge, they are information, and at times they even function as “restrictions.”
Established forms and systems of instruction such as “this is how you should walk,” “this is how you should run,” and “this is how you should stand” end up covering over the original voice of one’s own body.
But if one can return to one’s own axis, then one can know one’s own “correct answer” as a bodily sensation, without being bound by methodologies.
ippon blade is an experiential gateway for that.
Simply by standing, one can begin to see one’s own instability.
Simply by walking, one’s own wasted force begins to surface.
Simply by running, dormant muscles and sensations are awakened.
Precisely because it is the simple and austere structure of a single tooth, awareness of connecting center of gravity and axis becomes sharpened from the sole, through the pelvis and spine, all the way to the crown of the head.
Come to think of it, when I first encountered this single-tooth form, it was not merely sporting gear, nor was it a folk craft.
It was something that felt strangely nostalgic and yet utterly new, a kind of “guidance” that made me listen to the voice of my own body.
And from there, while falling many times and rising again many times, I continued to ask my body and mind, deeply and repeatedly:
Is this truly my movement?
Is this truly my life?
ippon blade is a philosophy of movement, and also a metaphor for the way one lives.
To stand, to walk, to run, to stop, to sway, to return.
In each and every one of those moments, the reality of oneself as life itself rises into view.
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Afterword | Everything I Put Into “The Single Tooth”
I did not walk this path by being taught by someone else.
By running barefoot, listening to the voice of my body, and at times stopping along the way, I was led as though by something invisible to develop the single-tooth geta ippon blade®︎, and together with my companions I have continued to expand this activity.
ippon blade is the crystallization of my own experience. It is also a prayer, and a wish.
So that anyone can return to their own center of gravity.
So that anyone can live naturally and without strain.
So that anyone can rediscover the being that is themselves through movement.
I hope that this one small tooth can become a bridge that connects, in a straight line, the heart, body, and soul of the human being standing upon the Earth.
And if, through this, you have come to pause and quietly listen to the voice of your own body—
that very moment is the complete answer to everything I have placed into ippon blade.
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ippon blade®︎ Developer / Profile
Takashi Kodaira / commonly known as Ten-chan
Born and raised in Tokyo, on July 7, 1977, at 7:00 a.m.
Currently 47 years old.
“The Milky Way galaxy, heaven is high.
Become a man of such scale that you could reach the heavens.”
He was born into this world as his grandfather’s seventh grandchild.
On Iriomote Island, he worked as a nature guide and marine shop instructor, running barefoot through the mountains and spending his days merging with the great natural world.
As he lived together with nature, the fixed ideas and conventional concepts within him began to collapse, and he started awakening to his true self.
At the end of 2012, he underwent an awakening experience.
He became deeply aware of the circulation and interconnectedness of all things, and of the inevitability dwelling within them.
The blood and soul of the ascetic mountain practitioners flowing within him quietly began to awaken to their calling.
One night, inside a UFO, surrounded by many cosmic beings, he was reunited with his late father.
That experience gave him conviction in his destiny.
At the end of 2013, carrying his life’s calling in his heart, he made his third fresh start in Tokyo.
While working as a sports trainer at a senior welfare facility, he began mountain climbing barefoot and in single-tooth geta.
He gathered single-tooth geta enthusiasts, organized training sessions, and also competed in marathons.
In April 2017, in Okuizumo, he became the first person in the world to complete a 100 km marathon in single-tooth geta.
That same year, while participating in the 100 km ultra marathon in Nikko, he entered an altered state of consciousness, and as he ran up Irohazaka, a whirlwind rose around him centered on his own body.
When he looked up to the sky from within that center, a crow tengu was fanning the air with a feather fan, stirring the wind.
That vision became the trigger for an idea descending into him: to design “a single tooth connecting heaven and earth” through the spiral structure of the Fibonacci golden ratio.
Soon after, he met the woodcraft artisan Mokuen, who ran 100 km barefoot, and development of the original single-tooth geta began.
In 2018, he moved to Hakusan City in Ishikawa Prefecture and continued his training.
He completed the Hakusan Shirakawa-go 100 km Ultra Marathon in single-tooth geta and completed ippon blade®︎ 369 (miroku).
It was released on November 11 of the same year.
After that, evolution continued:
• November 11, 2019: “ippon blade®︎ 1000 (ZEN)”
• February 2, 2022: “ippon blade®︎ ∞ (MUNI)”
Traveling throughout Japan, he has continued teaching body control and selling the product, sending more than 2,000 units of the series into the world.
Even now, his activities span many fields, including participation in marathons, lectures, and writing.
To date, he has completed three 100 km ultra marathons in single-tooth geta.
In November 2024, he moved to Haruno Town in Shizuoka, where tengu belief still remains.
Under the vision of “bringing the world into alignment through one tooth,” he continues deepening his daily path with the reintegration of body and soul as his theme.
ippon blade®︎ is protected by utility model registration and patents.
Written by: Ten Kodaira, also known as teng man
Returning to your axis is not the end.
It is where everything begins.
Movement gives it form.
Running brings it to life.
WE RUN TO BE BORN
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