Kai is a new investigator for Kanto region's narcotic bureau. When conflicted with anything that involves pain or extreme emotional hurt to him, Kai might switch to a violent alter ego who has no problem in harming others, though Kai himself is gentle and reluctant to do anything dangerous or hurtful to others. At first glance, Kai seems like a typical, happy young man, but when in danger his personality becomes violent and unstoppable. As Hal struggles to keep Kai in check, clues about Kai's past begin to surface, and he begins to wonder whether his violent mood swings may have something to do with the mysterious events that occurred sixteen years prior.