Kazuki's black kakugane, which powers his Buso Renkin weapon and keeps him alive, will soon advance to the point where it begins draining life from others around him. Teaming up with his partner Tokiko, Kazuki leaves on a mission to find out more about the black kakugane in hopes of keeping this from happening. Meanwhile they encounter an elite group of Alchemist Warriors that have been assigned to hunt them down and kill them!