Uruwashi no Kimi ~Anata no Naka ni Sasagu~

"I wanna date her...." Takuma is in love with Shiori. One day, Elena, a dropout succubus, suddenly appears in front of him and says, "I'll give you a hand." It seems if she fails this time, she will be expelled from her world. Takuma knows it is not fair, but he asks her to help him. Like this, he starts dating Shiori, who is beautiful, smart, and good at sports, and enjoys his school life. Any dream, however, ends sometime soon. What will happen to Takuma, Shiori, and Elena...?

[description by Honoohhh from Hongfire forums]