Yousei Jiken

Yousei Jiken (妖精事件, lit. "Fairy Data File") is a manga series by Yun Kouga.

Plot
Juria is a regular high school girl, wondering about love, sex and adults problems like the separation of her parents. One day, Ouji Amano the boy she has a crush on ask her to be his girlfriend and not only that, he wants her to be the mother of his child. What will Juria do? She is soon to know the world of the fairies since Ouji is more than just a boy.