After two years of lying dormant within Tsutomu Senkawa, Birdy is violently awakened by an accidental encounter with their old nemesis. As Birdy resumes kicking evil's ass, the dark secrets behind the experiments conducted by the "Agni" corporation are gradually uncovered. They appear to be experimenting with human body enhancement, producing what they term "beast men," to fight the alien invasions connected to Birdy.