Na mo Naki Tori no Tobu Yoake

From Storm in Heaven: Karasu is an angel of the class Powers; Shirasagi is a demon, a Marquis. One day Karasu is assigned to convince Shirasagi to return to Hell. However, Shirasagi doesn't act like a demon at all -- not only is he a priest, but he's forsworn the use of his demonic powers, and wishes nothing more than to live his life as a human. But the Archduke of Hell also has his eyes set on Shirasagi, and Karasu's own deviant behavior soon throws him out of God's favor. Will the pair be able to overcome the restrictions and laws of being an angel and a demon and live their lives freely?