Project Byrophyta was an attempt by the Chinese government to create an easily maintainable army of super-soldiers from the corpses of dead militery personell. Started just before the first contact with the Extemos on Earth, it was initially a success, with a full working batallion of troops deployed in North American to combat the Extemos scout. The project was ultimatly a failure, however, as the genome develped much faster then anticipated due to exposure to radition in an experimental reactor facility. This created a strain entirely seperate from the original project and resulted in the corruption of the entire populace of the test city. This, combigned with the pressures of the apocalypse on the government shortly thereafter, resulted in a complete abandoment of all materials related to the project. Left alone, the mutagen eventually developed sentience that took the form of a small child that refers to itself as "Bryo".
It occured that several people contracted both forms of the disease, resulting in a merging of the strains. These new half-breeds do not degrade, and operate as the project was originally designed to, but are completly subservent to Bryo. They maintain their sentience, however, and act independtly when not directly ordered by Bryo.