One night, Kazuki Muto jumps in to try to save what he thinks is a girl in distress from a monster and instead gets impaled through the heart. The girl, Tokiko, is actually an alchemic warrior with a Busou Renkin, name of Valkerie Skirt, with the mission to exterminate Homunculi. She implants the only other successful work of alchemy than the Homunculus, the Kakugane, to take the place of Kazuki's heart. The Kakugane resonates with his fighting spirit and forms a Busou Renkin (in his case a spear) so he can fight the Homunculus monsters who prey on humans. Kazuki joins with Tokiko to battle with the Homunculi and protect his friends and his sister Mahiro.
This series is the answer to a Bleach fan who hates watching all the filler episodes. It's fast paced, fun and overall a typical Shounen with short skirts, big swords and some weird little pink droid. It feels like a straight mix up between Bleach and Full Metal Alchemist, though I'm sure some of you would beg to differ. Either way; see it, save it, and savour it, because it has a great re-watch value.