Kikai

Monstrosity (奇怪, "kikai" in Japanese) is a dangerous and widely unknown substance in the Bleach universe. It is an incredibly powerful substance, with very limited information about it in any of the 's records. Of the information gathered by the, it is known that it requires a large and unforgivable sacrifice to be created. Because of the sacrifice needed to utilize it, monstrosity is considered taboo by the. Despite this, many still practice the creation of said substance, believing it will offer them a higher level of power.

Nature
Monstrosity is considered the "purest form of reiryoku." This is because it created by the sacrifice of spiritual beings, stealing the reishi that composes their bodies. Once stolen, the reishi is fused together; after the fusion, the spiritual particles become so compacted that they take on a physical form, which is that of a blood-red stone. Because of how much reishi is compressed into the stone, anyone that has a stone of monstrosity on their person (or within their body) is capable of feats unheard of in any of the spiritual realms. Although seemingly harmless, the amount of sacrificed beings must total over three hundred. For this reason, the creation of monstrosity is considered to be an illegal practice, with any shinigami caught doing so being executed without a trial.

Monstrosity users
Note: This list also tells of what said user utilized it for.
 * : Separation of the world/creation of the.
 * : Creation of the.

Behind the scenes
Monstrosity is largely based on the Philosopher's Stone|philosopher's stones from the anime/manga Fullmetal Alchemist.