Busou Renkin

The story opens with high‑school student Kazuki Muto being killed one night while rescuing a mysterious girl from a monster. He wakes up in his school dorm, convinced it was all a dream. Yet he soon learns the dream was real when a gigantic serpentine monster attacks him and his sister. Tokiko Tsumura, the girl he saved, explains that the creature is a homunculus. Kazuki had been killed by it during his attempt to protect her, but Tokiko, feeling responsible, revived him by placing a Kakugane medallion in his chest as a replacement heart. The Kakugane, Tokiko explains, is an alchemical device that, when activated, takes a form based on its user, formin…