Ripple

Hamon (波紋), also known as Sendō (仙道), is an ancient form of martial arts that serve as a core element in both Part I: Phantom Blood and Part II: Battle Tendency, acting as the main power the heroes utilized. It is also briefly featured in Part III: Stardust Crusaders.

History
According to Will Anthonio Zeppeli, only one in ten thousand bears the aptitude capable of utilizing Hamon, and the main characteristic of driving Hamon comes from the pressure one has felt through harsh situations in life. Those who are not capable will still be able to use Hamon, but only to an insignificant extent.

Hamon seems to have been created at the dawn of humanity with the purpose of fighting off the Pillar Men's influence on the world. This also includes the creation of minor demi-humans, known as vampires and zombies, created through the Stone Masks, and stopping them from ever achieving perfection through the Red Stone of Aja. Hamon users have built many devices and temples across the world to help them train and learn from one another.

Techniques
Hamon is based on using the energy of the sun's rays through breathing and empowering the body with "ripples" of solar energy. While it can be used to destroy vampires and zombies, it can also affect non-living things. An object, while charged with Hamon energy, will become more dangerous, and its user can perform several techniques that can combine with the warrior's own tactics, to allow for a very flexible fighting style. Ordinary humans can also be affected by Hamon attacks, as Caesar had used his Hamon to control a woman into fighting Joseph before he had undergone the final stages of his training, and Joseph's trained Hamon would have caused an ordinary person to feel pins and needles before fainting, similar in nature to heavy exposure to the sun's rays. Kars' Hamon energy, boasting several hundred times Joseph's power, caused Joseph's flesh to melt. Hamon is also transferable between users, as both Will A. Zeppeli and his grandson Caesar transferred their Hamon to the protagonists they were aiding shortly before their deaths. Hamon users can reject harmful substances inside of them by ejecting it from their bloodstream with the use of Hamon energy.

Because of its versatile nature, many warriors use different weapons ranging from a scarf, bubbles, wine, and even Clackers (in this case a pair of steel balls connected to a rope). Many of the most powerful techniques are classified as "Overdrives" (lit. "Hamon Rush"), and are often color named for the medium they're used with (Metal Silver being one to transmit through a sword). An object that is impacted with the force of the Overdrive will carry Hamon energy through it, and will become lethal to the vampire's touch; this can be used to strike an enemy in another room by breaking through a wall and causing its solar energy to disintegrate the target.

Liquids conduct Hamon especially well (and the user's Hamon shows on liquids as actual ripples), and it can even be used to increase the surface tension enough to allow the Hamon user to walk on water. It was mentioned by Joseph that objects covered in oil can conduct Hamon much easier. Joseph was also shown to be able to cover his body in Hamon energy by channeling through his own Stand; it is unknown if a humanoid Stand like Star Platinum, belonging to his grandson Jotaro, could do the same.

Weaknesses
While the Hamon users can make the most simplistic of objects into lethal weapons and become themselves dangerously powerful, they are not without weaknesses. A hamon user must be able to constantly breathe, if this breathing is stopped or reduced due to injury they slowly grow weaker to the point that they can be easily defeated even by a zombie. This weakness was exploited by many vampires, the main one being Dio, who mortally injured Jonathan and in the process prevented him from using Hamon. Dio had also discovered, that removal of heat from a Hamon user causes their blood to move slowly and, makes them unable to attack as rapidly and effectively as before.

Connections
By the start of Part VII: Steel Ball Run, which takes place synchronously on the timeline of the alternate universe as Part I: Phantom Blood took place in the original universe, a similar power called the 'Spin' is introduced. This technique is first seen used by Gyro Zeppeli, but is soon sought out by Johnny Joestar, who believes that the Spin will allow him to walk again.

Hamon and the Spin are very similar, mainly in that the Spin makes use of the Steel Balls, which makes it as versatile as Hamon, if not more so. Gyro has been able to use it to deflect a bullet with his skin, provoke muscles to do involuntary actions, and price impact of a persons body. The Spin's power derives off the Golden Rectangle, a mathematical formula which allows for an object to spin nonstop in a divine rectangle. It is possible that the Hamon has some connection to Gyro Zeppeli's Spin technique.

Trivia

 * According to Araki, the concept of "Rules" and psychic powers in the manga, Babel II by Mitsuteru Yokoyama helped him form the basis around the idea of Hamon.
 * The English dub of the OVA translates Hamon as "Wave Energy."
 * Hamon-based moves, such as the Overdrive, form the basis of some of Joseph's techniques in the Capcom fighting game, as well as the entirety of Young Joseph's moves. When performing these Hamon moves using the strongest attack button, both Josephs can be seen visibly breathing.