Summary:
One night Kazuki Muto tries to save a girl from a monster, but gets impaled through the heart. The next day he wakes to find that it was only a dream. That is until he finds out that it is all true when a creature called a Homunculus attacks him and his sister. The girl, Tokiko, Kazuki saved the night before, comes and fights the creature. Kazuki finds out Tokiko is a alchemic warrior and that he did in fact die but Tokiko put in a Kakugane in place of his heart. Now infused with his fighting spirit the Kakugane forms a Busou Renkin so Kazuki can fight the Homunculus, along with Tokiko, that prey on humans.
