Tenshi no Hane to Akuma no ShippoTen-Hane; Angel's Wings and Devil's Tail; てんしのはねとアクマのシッポ

From Aerandria: The story begins from the moment a young devil boy transfers to an Academy for angels located deep inside the forest. He was tasked to clean out the monsters in a nearby forest but after successfully doing so, the angels asked him to become the Academy's Knight to prevent a 'great catastrophe!' Sounds great! But, wait... a devil who's a Knight in an Academy for angels?!