Ripple

Hamon (波紋), also known as Sendō (仙道), is an ancient form of martial arts.

Through self-controlled respiration, Hamon links trained persons with the energy of the Sun; in polar opposition to the energy exerted by Vampires, Zombies and the Pillar Men.

Hamon is the main source of power for the heroes of Part I: Phantom Blood and Part II: Battle Tendency. It is also briefly featured in Part III: Stardust Crusaders.

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 experience a pins and needles-feeling before fainting - similar in nature to symptoms experienced after prolonged exposure to the sun's rays. Kars' Hamon energy, boasting several hundred times Joseph's power, caused Joseph's flesh to nearly instantly 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", 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 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 even the most simplistic of objects into lethal weapons and become themselves dangerously powerful, they are not without significant weaknesses. A Hamon user must be able to constantly breathe: if this breathing is stopped or reduced due to injury or other conditions, they slowly grow weaker and lose the ability to create more Hamon energy, to the point that they can be easily defeated - even by a mere zombie. This weakness was exploited by many vampires - notably when Dio mortally injured Jonathan, piercing his trachea and in the process preventing him from using Hamon. Dio had also discovered that he could flash-freeze a Hamon user in seconds (he even claimed to be able to freeze Jonathan whole in just two seconds), causing their blood to flow slowly to an eventual stop, making them unable to attack as rapidly or disabling them outright.

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.

Similar Phenomena in Part VII
In the new canon beginning with Part VII: Steel Ball Run, a power called the Spin is introduced, similar in a few notable ways to Hamon; as part of a series of parallels to concepts native to the original canon.

Channeled by Gyro Zeppeli with special Steel Balls and by Johnny Joestar with a Stand power that spins his nails, the Spin enables a range of effects on the environment and the body.

Trivia

 * Araki has mentioned engaging in a morning breathing routine (perhaps like Qigosiming).
 * At the beginning of Thus Spoke Rohan Kishibe - Episode 6: Poaching Reef, Rohan Kishibe engages in a breathing exercise.
 * 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 is similar in concept to the concept of Qi found in other manga and anime.
 * Hamon-based moves, such as the Overdrive, form the basis of some of Joseph's techniques in video game Heritage for the Future, 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.
 * Hamon also has medicinal usages, such as being use to effectively counter and reverse gangrene.