Devil & Devil 

The continuous struggle of good and evil, angel and devil respectively, still ensues and neither one of them wants to give up. The story is about a devil named Sword who has an angel rival named Io. They fight to the point that in their 101st battle, that they severely wounded each other and both fell toward Earth. Having deep wounds but not wanting to die, Sword looks for a body to be able to possess. He somewhat finds a thoroughly, beat-up, unconscious boy thus he entered it allowing him to live. He eventually finds out that the body he possessed is far too weak- in short a nerd. Furthermore, his rival Io also possessed a body in order to survive, unfortunately, it's the twin brother of Sword's host which is the opposite behavior- violent. Not only that, they cannot use each of their own power! Being opposite of their behavior's host, problems are escalating. But Sword has bigger worries, both devil and angel are after him, what will happen now? (Sourc: Anime-Source)