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.
In many ways, the show is somewhat generic. The story, fight scenes and characters aren't very unique compared to some other shows. Despite the lack of originality, the show is a lot of fun to watch. I usually find the jokes in shonen series to be too corny to enjoy, but for some reason the humor and action intertwined perfectly in this series for me to enjoy the entire thing. Also, the formulaic story prevents the writers from introducing anything confusing or distracting. All in all, I would recommend this show to someone who is looking for something fun to watch and is not expecting an intricate plot. Don't be tempted to compare it to FMA because the title has alchemy in it... the two series are not that similar.