Equivalent Exchange

Equivalent Exchange (等価交換) is the blanket term for a type of phenomenon featured prominently in the eighth part of the JoJo's Bizarre Adventure series, JoJolion.

Taking on a variety of forms over the course of the part, the concept of equivalent exchange has become a central plot point in the part's overall narrative.

Summary
Equivalent exchange is the ability for one thing to be traded for something else of equal value. However, the exact mechanics of this principal's application differ depending on how equivalent exchange is induced. Beyond its various supernatural incarnations, the underlying idea of exchanging one thing for another is a recurring concept present in JoJolion. Notably, the "birth" of Josuke is a result of his two previous identities being permanently lost. This indirectly echoes the sense of responsibility shared by parental figures of the Higashikata family, who on multiple occasions have demonstrated a willingness to sacrifice their own health in order to cure a loved one of the family's unique hereditary illness.

Wall Eyes
The area around where the Wall Eyes formed (notably on and around the Higashikata estate) possesses a property that can result in Equivalent Exchange under the right conditions. If two subjects are buried together in close proximity to one another, they will undergo exchange with each other, trading seemingly randomly selected parts for other parts of equal value. A notable example of this type of exchange is demonstrated by Kei Nijimura, who bisects a lemon and a tangerine that had been buried near the Higashikata estate, revealing that corresponding segments of both fruits had been swapped out for one another. So far, this method of exchange has only been demonstrated on organic matter. It is unclear whether or not this type of exchange is possible for things that are inorganic.

As stated by Kei, the Higashikata family has been aware of this method of exchange for generations. This knowledge is demonstrated in that through unknown means, this type of exchange can be used to transfer the Rock Disease from one host to another.

Exchange via the Wall Eyes ultimately led to the creation of Josuke Higashikata after his two former identities were buried near the Wall Eyes in the midst of Kira being healed by the New Locacaca he and Josefumi had cultivated. It should be noted that while this type of exchange is seemingly equivalent, the matter which is exchanged does not always directly correspond (the most notable example being the fact that Josuke retains both Josefumi and Kira's pairs of testicles post-exchange).

Locacaca
The fruit of the Locacaca tree is also able to cause exchange when eaten. Upon being consumed, the Locacaca will target and heal a specific injury, turning another part of the patient's body into stone as a collateral effect. The body part sacrificed is determined by the Locacaca, seemingly at random. An example is when an old man uses the Locacaca fruit to regrow his lost leg in exchange for his eyesight. Apparently this process can be repeated as long as someone has a fruit, continuously sacrificing random parts of their own bodies in order to gain back what they had lost in the previous instance.

Locacaca 6251
The Locacaca 6251 drug developed by members of the T.G. University Hospital staff is able to maximize the healing properties of Locacaca exchange while minimizing the risk of an important sense or organ being sacrificed.

New Locacaca
The New Locacaca created by Josefumi Kujo and Yoshikage Kira is able to perform Equivalent Exchange without sacrificing part of the host's body; instead someone in direct contact with them can be given all negative side effects of exchange. This fruit seemingly functions as a mid ground between the two other kinds of exchange.

Upon eating an unripe fruit from their grafted Locacaca branch, the dying Kira's injuries were healed, while parts of Josefumi's body turned to stone, beginning with the areas that had been in contact with Kira upon eating the fruit. However, upon eating the seemingly ripe new Locacaca grown by Jobin Higashikata, Yasuho Hirose experienced a different kind of exchange: upon her arm being regrown Joshu (who had used himself as collateral in the exchange) had his own corresponding arm shrivel up rather than turning to stone.