Niizuma wa Mahou Shoujo

Mai comes to the human world to make 100 people happy and thus become a full-fledged witch. She only has 5 people left! One day she gets spotted and prepares to erase memories as usual, but Koutarou sincerely encourages her instead of behaving creepy, so she does no such thing. Mai helps to solve Koutarou's problems with classmates and teachers, but eventually the bond intensifies, and they start to live as a couple.

[From vndbreview]