Some things in life are so bad that you'd like to pretend they're just a dream. Unfortunately for Kazuki, trying to save a strange girl from being brutally killed by monsters (and ending up dying instead) is an unfortunate reality. Out of pity, the girl replaces Kazuki's heart with an alchemy-based artifact known as Kakugane, so that he may live on. With this strange device, Kazuki gains the power of Busou Renkin -- Arms Alchemy; a power that will come in handy when monsters (and worse) begin to plague his town! Kazuki soon meets the girl from his “dream” (named Tokiko) in reality, and she tells Kazuki to get on with his life; but with his sister and friends in danger, that might not be possible. Besides, if Kazuki gives up the chance to show off just how manly he can be, how can he hope to win the heart of the alluring older-sister-like Tokiko?!