Subaru moves into a dorm and against his wishes becomes part of a Happy Set! But, with his allergies for cats and Sei's love for them, will the two ever really become a Happy Set...?

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?!