らいでぃんぐ いんきゅばす

Kazuya is a high school student. One day, he finds a key at an old church while he prepares for Halloween. The key is big and looks beautiful. Actually, it is a key to release Riru, an incubus. To express her gratitude, she kisses him, and they start living together. His life dramatically changes, involving his friends. What will happen to him in the end...?