The Spin is a state of rotation defined by its closeness to perfection, that perfection being the Golden Rectangle (黄金長方形, Ōgon Chōhōkei), more specifically the Golden Spiral that
is derived from the Rectangle, a mathematically endless spiral, and a feature said to be omnipresent in the surrounding nature and a fortiori in works of arts.
Unlike the average rotation, the Spin is persistent and produces more rotational energy than it takes to create. That rotational energy is transferred to nearby objects in the form of vibrations and can be wielded for a wide array of purposes.
The Spin is a specialty of the Kingdom of Naples. It is intensively used there either for medicine or for battle. All characters capable of performing advanced Spin techniques are either Neapolitan or have been taught by a Neapolitan.
Using the Spin
Gyro explains the Golden Rectangle to Johnny
Because of its miraculous property, the Spin has been wielded as a technique by a chosen few at least since the Middle Ages from which several specialized skills have been derived.
Users of the Spin typically try to spin objects to follow as best they can the Golden Rectangle, creating a near endless rotation that may then create an infinite amount of rotational energy, before throwing said objects at a target. To do so, they apply a small force causing the object to Spin near perfectly, giving it an impulse of energy to start the rotation, and then let the rotation perpetuate itself. A bit of advice given to neophytes is to visualize the perfect rotation and then try to emulate it.
The Spin is deceptively and relatively easy to learn at the basic, as the novice Johnny Joestar manages to produce a conclusive Spin with a cork within a day of learning about the power's existence; however, it is extremely difficult to master. The Spin must be imbued into a medium that will keep on spinning and must be thrown so the object can transfer the energy through contact. Thus, a Spin user must be able to expertly aim and throw objects in order to hope for a result. One must also know the human body extremely well to exploit the effects of the Spin on people to the fullest. For instance the Zeppeli Family are trained as surgeons to use the Spin on criminals on death row, otherwise, the Spin may only result in a simple enhancement of destructive energy. Others like the members of Naples' royal guard only use a highly specialized application of the Spin on the human body.
Gyro throws a Steel Ball at Diego Brando
The Spin naturally enhances the destructive power of a projectile and thus can be thrown to simply inflict damage. A Steel Ball imbued with the Spin can destroy great chunks of rocks. Wekapipo's satellites are also propelled with as much force as bullets, being able to tear Gyro's hand.
The Spin can affect the body to harden it and enable it to easily transmit energy somewhere else, granting supernatural but temporary sturdiness. It allowed Gyro to become bulletproof and withstand the blast of one of Boku no Rhythm wo Kiitekure's bombs and only harm his leg or Wekapipo to redirect the energy of a Steel Ball.
The Spin is partially used to take control of the projectiles it is imbued to. Thanks to this phenomenon, Users of the Spin have control over how their projectiles react and can aim better, yet also have the projectiles return to their hands so as to not waste them.
An object imbued with Spin can be used to reinforce the Spin of other projectiles, for instance increasing the effective range of the Steel Balls.
Spinning objects have a high rotation speed and thus can create a large amount of friction. Thus, they can maintain objects in place like a cape to function like a sail or unravel objects like a tree's bark. Steel Balls, in particular, are shown to create makeshift ropes, and even carve into metal to create bullets.
More specifically the Golden Spiral that is derived from it, the Golden Rectangle is the perfect state of the Spin. It is a mathematically endless spiral, and a feature said to be omnipresent in the surrounding nature and a fortiori in works of arts.
Hemispatial Neglect is a condition applied to the opponent as a result from one of the satellites from Wrecking Balls, a type of Steel Ball that is also associated with the Spin. It causes victims to lose all sense of feeling on their left side; in other words, victims can't feel or even see their left side.
The Golden Spin is a superior state of rotation that only the masters of the Spin can use. To use the Golden Spin, one must approach the Golden Rectangle, a rectangle with a proportion equal to the golden ratio (approximately 16:9) that when recursively divided into a square and another golden rectangle, traces the path of the Golden Spiral; a self-similar and thus endless spiral. Used as a scale, the Golden Rectangle allows the creation of a perfect rotation and thus an infinite amount of energy. The Gold Rectangle is actually observable in nature, from the wings of a butterfly to the shape of a tree to snowflakes, and by extension in works of arts.
Gyro's Belt Buckle is notably shaped in the proportions of the golden rectangle and can be used as a model. The Zeppeli Family regularly uses the Golden Spin thanks to their knowledge of the golden ratio. Gyro then taught Johnny how to use the Golden Spin, allowing the latter to achieve greater forms of his Stand.
One can prevent Spin Users from using the Golden Spin by choosing the right battlefield, one that is devoid of life so that there is nothing that a Spin user can observe to discern a golden rectangle. For instance, Wekapipo and Magent Magent ambush Gyro and Johnny in the middle of a frozen strait.
Colloquially referred to as the Super Spin, this variant is a superior version of the Golden Spin which involves riding on horseback. This technique represents the most faithful emulation of the golden spiral humanly possible.
Developed in the Middle Ages to bypass the shield and armor of mounted knights, stirrups were invented to harness the power of a running horse. The horseman must let the horse run with the force of the Golden Rectangle, meaning it must gallop at its most natural speed. At this perfect pace, the horse spontaneously creates the energy of the Spin; it can then be harnessed through the stirrups and passed on through the body, into the arm and wrists to further empower the throw of the Steel Ball. Thus, a truly perfect rotation emitting an infinite amount of energy is created. The Golden Spin is associated with the power to produce gravity, the only force supposedly capable of going between dimensions.
Unlocking the Golden Spin on horseback grants mastery over an infinite amount of energy, therefore, several miraculous feats are possible. First and foremost is that its wielder spontaneously develops a Stand or evolves it should they already have one. Gyro manifests the Stand Ball Breaker, while Johnny develops Tusk's final evolution: Tusk ACT4.
Although it is almighty, the horseback Golden Spin is incredibly complicated to set up. One must not only have a healthy horse, but also have the expertise to feel when it runs at its natural pace, in addition to the need of being proficient in the Spin and possessing a projectile that can be imbued with the Golden Spin. An imperfect thrown sphere will result in a failure and any interference during the horse mounting, like bumping into an obstacle or the horse being attacked, will completely interrupt the process. During the events of Steel Ball Run, only two people on Earth could reproduce the Golden Spin on horseback. There exists a workaround for setting up this technique. Johnny uses a Steel Ball on his horse's leg, making it kick him with the energy of the Golden Spin. Johnny was thus imbued with the energy of the Golden Spin and by spinning his nail at the same time, could reproduce the same infinite Spin he would have by riding his horse.
Ball Breaker manifests whenever an experienced Steel Ball user performs the Zeppeli Family's ultimate throwing technique. Though considered a Stand, it is purely a visualization of Spin energy. Being an embodiment of the vast quantity of energy collected by a Steel Ball, the "Stand" is shown being capable of accelerating aging.
Soft & Wet's soap bubbles are actually thin lines that spin rapidly; the lines are so thin that they are close to zero, therefore considered nearly nonexistent. Because of this, they are capable of bypassing any kind of logic in the world, including calamity. These spinning bubbles can also be used as weapons that explode on contact, as inherited from the Stand's late fusion with Killer Queen. After discovering these aspects, Josuke develops a new ability, which he dubs "Soft & Wet: Go Beyond" (ソフト＆ウェット・ゴー・ビヨンド, Sofuto Ando Wetto Gō Biyondo). Go Beyond's Explosive Spin bubbles first manifest from Josuke's birthmark, and then are shot out from his fingertip. However, due to the bubbles being invisible and "nonexistent", it's difficult for Josuke to aim Go Beyond, and therefore requires Paisley Park's help to direct the bubbles.
The Spin has been long studied as a human anatomical corrective and medical treatment by the Zeppeli Family, doctors renowned throughout Italy but also royal executioners of the King of Naples. They employ a generalist form of the Spin with Steel Balls thrown at targets, granting them a wide array of uses, although their careers orient them toward affecting the human body.
The royal guards of Naples use a highly specialized and aggressive version of the Spin, using Wrecking Balls instead of simple spheric balls. The smaller spheres embedded in the Wrecking Ball act as extra projectiles that can suddenly spring out of the main sphere and can attack multiple targets with precision and from unexpected angles. Moreover, even if the satellites miss their target, the shockwave they create in their passage causes hemispatial neglect, crippling the opponents in battle and allowing Wekapipo or allies to hide from the enemy.