Koilanthropy is a condition discovered and named by Sumiko Hadashi which causes Shinigami to temporarily transform into hollow-like-beings. An infected Shinigami is called a Koilanthrope. Koilanthropy is similar in nature to Hollowfication. The virus that causes Koilanthropy is unknown but is present somewhere in the flesh of hollows.
Koilanthropy is transmitted when a Shinigami ingests large amounts of hollow meat. A virus then infects the blood stream and tissues within the host turning them into a Koilanthrope. The virus is currently incurable using currently developed methods. It is not transmissible from one Shinigami to another short of a blood transfusion.
Koilanthropes have two forms, Dormant Form and Viral Form. Which form a Koilanthrope takes depends on a few factors and are mostly dependent on the infections phase (detailed below).
Dormant Form is the default state and is mostly indistinguishable from a regular Shinigami.
A hollow like state that Koilanthopes take due to the virus. The hosts body is immediately wrapped in a heirro like chrysalis and rapidly covers the host in Heirro (takes only seconds to complete). The Koilanthrope emerges from the chrysalis in their viral form which resembles a hollow with the exception of a hole, which Koilanthropes do not posses. Koilanthropes all develop one bio-weapon, which is a form of attack that is usually a mutation of their own body or spirit. Koilanthopes, being imperfect beings, do not posses many extraordinary powers but they have been shown to Shunpo and some have access to Reiatsu based abilities but it's rare. Koilanthopes cannot cero as they are not true hollows. While in Viral Form, hosts have no control over their actions and act on the viruses instinct alone, becoming no more intelligent than that of a feral animal.
Phase 1 - Initial InfectionEdit
Upon contracting Koilanthropy, the host enters phase 1 of the infection. Phase 1 is rather short, involving only the time it takes for the virus to completely infiltrate the host. Upon complete infectivity, the host will immediately take Viral Form for the first time and must feed on reiatsu-dense substances to sustain itself. If the host does not feed during this time, (roughly about 24 hours after entering Viral Form) the infection will die and the host will become immune to all further infections. If the host feeds successfully they will enter phase 2.
Phase 2 - IncubationEdit
The intermediary phase, Incubation lasts an extremely long period (Anywhere between 6 months to 4 years) and the virus becomes incurable upon entering this phase. During phase 2 the host must feed on reiatsu-dense substances regularly. To reinforce this behavior, the host will perceive that all non-reiatsu intensive foods taste like ash but it's purely a mental symptom, there are no negative side effects to eating regular food. Failure to feed on a regular basis will cause an outbreak and the host will resume Viral form to sustain it's hunger. The duration of phase 2 relies on how much reiatsu the host consumes. Once the virus has consumed enough, it will progress into the 3rd and final phase.
Phase 3 - AssimilationEdit
The final phase occurs when the virus has matured enough to attempt to take over it's host. For this to complete successfully, the virus must take over the hosts mind (and in turn, inner world) to successfully assimilate the host and acquire it's body. If the virus successfully takes over, the host will take Viral Form and slowly the hosts cells will be replaced by the viruses own (the heirro serving as a cocoon). Given enough time, the shinigami will die and the virus will assume complete dominance of the body. This process can be delayed by shattering the mask of the Koilanthrope, temporarily allowing them to resume Dormant Form if their cells have not yet been replaced. Any cells already replaced cannot be healed.
"Beware that, when fighting monsters, you yourself do not become a monster... for when you gaze long into the abyss. The abyss gazes also into you."
Yamashita Ritsu - Thanks to the mental walls formed in Yamashita's mind, he has been able to survive phase 3 by preventing the virus from taking over his inner world. These mental walls, formed by his amnesia, serve to separate his conscious mind from the virus allowing him to operate freely with little symptoms. His right arm however has already been replaced by hollow cells and can never return to normal. The mental walls are not perfect however, as it requires a lot of mental control on Yamashita's part and as such, too much emotional stress can cause these walls to temporarily fail forcing Yamashita into Viral Form. The only way to undo this is to knock out Yamashita or break the hollow mask and give him time to rebuild the mental walls. It is unknown how long Yamashita can survive in viral form before he is assimilated making transformation extremely risky.
Yamashita's rare condition gives reason to believe that hosts can survive Phase 3 with power of will alone. If the host can effectively keep the viruses infection of the mind at bay then they should be able to live rather normally.