Kazuki Azuma returns to Japan after ten years away, only to be chased down by the Bubuki police. He's saved by a childhood friend, Asabuki Kogane, and her right-hand-shaped Bubuki. He then meets the Bubuki users Nono Hiiragi, Ougi Kinoa, and Taneomi Shizuru. Azuma has never even heard of Bubuki, but after learning that he's the user of the "heart" Bubuki, he makes his way to the Buranki prison in Shinjuku's underground to awaken the sleeping Buranki called Oubu.