Name: Kaibutsu (Experiment P4)
Japanese name: P4
Sex: Male
Breed: Unknown (Mutant)

Kaibutsu is the result of science's research in gen manipulation. Kaibutsu's genes and DNA has been manipulated to create the monster he is. He escaped from the scientific institute called P4 (which is also his scientific name) and promised to kill all the scientists who had been close to him.

He now hides in the Ou mountains, where he kills all humans that come by and everyone else who stands in his way. He fights Weed and the English setter, Smith in the depths of the fortress Gajou. Here he kills Smith and gets buried during a rockslide.

Kaibutsu survives and fights even more furiously than before. He kills Jerome's soldiers, North, Robert, Rocker and Heuler before Weed, Ken, Kagetora and Jerome himself finally overpowers him and push him off a cliff. Kaibutsu lands on a sharp branch which kills him by piercing his heart.