Oroka na Tenshi wa Akuma to Odoru

Summary:

Akutsu Masatora is a demon who has infiltrated a high school in the human world. His goal is to find candidates to aid Hell in the fight against their natural enemies, the angels of Heaven. Assigned a seat next to Lily Amane, another student who transferred here not long ago, Akutsu falls prey to her beauty and decides to recruit her to his cause. But there's more to Lily than meets the eye, and Akutsu not only finds himself an accomplice to one of the very enemies he is supposed to defeat, but he also might have developed feelings for her.