18+ Senpai ga Boku ni Shiteru Koto

The Asahigaoka Academy—a prestigious all-girls school known for its quality education—recently shifted to a co-ed style of education for its junior high school division, whilst its senior high school students are still all girls. Tatsumi Naeda is one of few boys enrolled for the new term. Shy and somewhat reserved, he has a hard time getting used to his surroundings, only finding some solace in the quiet of the literature club where he spends his time with its sole member, Yuno Tsuyuri, and freshman student in senior high. But little does he know that Yuno's lack of relationships with a man has given way to an insatiable, sexual urge.

(Source: Irodori Comics)