Busou Renkin

A high school student named Kazuki Muto saves a girl from a monster and dies in the process, only to awaken believing it was a dream. He later discovers the event was real when a large monster attacks him and his sister. The girl he rescued, Tokiko Tsumura, reveals the creature is a homunculus and explains that Kazuki was killed during the rescue. She revives him by placing a Kakugane medallion in his chest, acting as a new heart. The Kakugane is an alchemical device that forms a unique weapon called a Buso Renkin when activated, tailored to its user. Kazuki creates the "Sunlight Heart," a large lance, while Tokiko wields the "Valkyrie Skirt," an execution scythe. Together, they fight against homunculi and their master.