Three years ago, mutant demons began appearing in Japan. While some are harmless or helpful towards humans, others are troublesome. Created from humans suffering from extreme emotional distress or unresolved trauma, these mutant demons began to wreak havoc as they began to evolve to be more intelligent and dangerous.
A lone rooster named Keiji wanders around various cities of Japan while defeating mutant demons he encounters. His ultimate goal is to find and kill the mutant dubbed "The White Demon" who killed his sister in order to avenge her death.