Kawaikereba Hentai demo Suki ni Natte Kuremasuka?

Keiki Kiryu, a second-year high school student, is like any average male in their teens. He really wants a girlfriend. He's a member of the calligraphy club and usually helps out in the school library. One day while cleaning up the club room along with his sister (Mizuha), fellow club member and senior (Ayana), freshman library assistant (Yuika), and fellow classmate (Mao), an interesting thing happened. While everyone except for Keiki going home, he finds a letter on top of the club desk. Not just a letter but a love letter addressed to him by an anonymous secret admirer. He also finds a pair of panties to go along with it. Overflowing with emotion (and possibly testosterone) he sets off to find his "Undierella" and finally get his wish fulfilled. However, while looking for his admirer, he comes to find out some secrets that each candidate is hiding.