The Kodoku Virus (tentative) was a part of a bioweapons research project led by Alex Wesker. She performed this research on the island Sonido de Tortuga, the place having been the site of a facility owned by Spencer. It was from here she was instructed to create his immortality virus to stave off his death, but she advanced the Kodoku Plan instead. She eventually left permanently for her stronghold on Sushestvovanje Island to perfect t-Phobos and the mind-transfer experiment, and left the Kodoku Plan to her researcher, Dirk Miller. He killed the other researchers and posed as the island's mysterious shaman in order to acquire both guards and test subjects from the superstitious natives. When Spencer investigated, Alex had left and her personnel were nowhere to be found.
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Kodoku in Japanese (originally Chinese) mythology is a ritual where an assortment of different creatures are pitted against each other, with the lone survivor said to carry a powerful curse. The Kodoku Virus, therefore, was injected into test subjects, and the resulting mutants would battle until only a single survivor remained. The best mutant would have the recombinant strain extracted from it, which would be used for a new trial of testing, until the perfect virus was created.

A Shén Yā Pharmaceutical agent named “Zǐlì” (or Julie) was sent to steal the Kodoku Virus, along with fellow agent Mike Seaman. She killed Dirk Miller and acquired the only sample of the finished virus, but was forced to inject herself with it to survive fatal injuries. After her mutated form was completely obliterated, Kodoku was presumably lost. However, Kodoku Zombies still roamed the island, which was quarantined and left alone by the BSAA, presenting the possibility of the virus once again being recovered in some form.
Effects
Some things can be inferred about the Kodoku Virus: Morio, of the mutants, very clearly is meant to resemble the T-002. From this it can be deduced Kodoku is not only based on the t-Virus, but that live hosts (like Morio, Schraube Dämon, and Monster Zǐlì) are actually Tyrants. By making said Tyrants battle each other, the most intelligent, strongest, and resilient variations are singled out. As the virus passes from host to host new mutations emerge and are singled out in the best hosts, until the most desirable mutation is achieved.
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Kodoku creates Tyrants from any host and from merely injecting them, like t+G, without the need for body strengthening surgeries or special genes. This allows for cheap creation costs as opposed to mass production via cloning. Like the G-Virus, infecting corpses creates Zombies, as dead hosts cannot undergo the necessary transformations.
The mutant Morio constructed a makeshift village inside of a cave in an effort to reclaim his time as a human, and so began killing natives and tourists, dragging their bodies off, and infecting them to create Zombie residents. Some of these Kodoku Zombies wandered off and started an outbreak. |
Kodoku Tyrants and Zombies are more intelligent than their t-Virus counterparts. Zombies have been known to retain small memories, but the ones created by Morio acted like they did in life in the absence of food. Brown was capable of some speech and free will in the early stages of transformation. Kodoku Zombies seem somewhat more coordinated as well, being able to swim and climb onto a boat. The trend of "smart" zombies is very common in modern, advanced virus strains, as seen in C and A. This is likely due to improvements to the issue of brain cell rejection and necrosis.
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Morio (formerly known as the native Eliseo Mabou) itself tried to be human again with its village, and clothed itself and fashioned weapons from an anchor and harpoon (Morio is a Japanese play on words, referencing both "Monster" and "Harpoon". This name was given to it by the survivor Takeru Tominaga). It also sought to protect its former sister, Marilou. Despite this, it continued to follow its programing to ensure transportation off the island was cut off. Morio was later killed by a rocket launcher blast after being injured by Monster Zǐlì.
The Schraube Dämon (German for Screw Demon) was created from the islander López. It used boat screws and later a drill with its extra set of arms, and both it and Monster Zǐlì had reptilian-like skin. This could be a random mutation, a result of recombination, or a result of reptile DNA being inserted into the virus. Schraube Dämon was killed by Morio.
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Monster Zǐlì's body had become inverted, like the Glasp B.O.W. This, I believe, is due to her body breaking from a fall just before she injected herself. Her broken bones were mended and grown out in unnatural and forced positions, like a broken bone set incorrectly, resulting in a twisted body. She had bladed tentacles, could survive as a decapitated head, and despite being the largest of the three mutants, was incredibly fast and agile. She retained her intelligence, even being capable of speech, but was so aggressive she killed her allies from Shén Yā Pharmaceutical. Zǐlì’ severed yet autonomous head was destroyed by a grenade lodged into her mouth.
Pictures of Biohazard Heavenly Island taken from MangaOwl.