Erementar Gerad

During a routine raid, sky pirate Coud Van Giruet discovers a most unusual bounty: Ren, an "Edel Raid", is a living weapon who interacts with a human to become the ultimate fighting machine. But when Ren is captured by an evil Edel Raid dealer named Beazon, Coud quickly realizes that she is even more prized than he first thought. Ren's only chance of rescue lies with Coud and the agents of Arc Aile!
(Source: Digital Manga Publishing)