Busou Renkin

The story begins when high school student Kazuki Muto is killed one night saving a mysterious girl from a monster, only to wake up in his school dorm, believing it to be a dream. However, he soon finds out that dream wasn't a dream at all when a giant serpent monster attacks him and his sister.

Tokiko Tsumura, the girl he saved, explains that the monster is a homunculus. Kazuki had been attacked and killed by it when rescuing Tokiko, however, feeling responsible for him, she revived him by placing a Kakugane medal in his chest, serving as a replacement heart, or "New Life".

The Kakugane, as Tokiko explains, is an alchemical device that, when activated, takes a certain form based on the Kakugane user, forming a unique Busou Renkin(Arms Alchemy). The Busou Renkin is the only thing that can destroy a homunculus monster. Using this, Kazuki creates his own Busou renkin, taking the form of a giant lance, later named 'Sunlight Heart'. Along with Tokiko and her own Busou Renkin (the Valkyrie Skirt, scythe blades attached to her thighs), Kazuki joins the fight against the homunculi and their master.

Thus, Kazuki becomes an Alchemy Warrior, he trains to become stronger to fight Homuculi. But he runs into another student at his school that creates Homuculi and learns the duties of being an Alchemy Warrior.

The story continues with tracking down the Alchemist Organisation’s enemy. Victor.