OnaTra! ~Onaidoshi to H na Training~

Nanami looks smaller than classmates. She only gets along well with Keisuke who lives next door and attend the same library committee. One day Nanmi witnesses Keisuke having sex with his cousin Itsuki, and she starts masturbating every day. But it can't satisfy her already, so she urges Keisuke to get into relationship...

[From vndbreview]