18+ Boku no Seito wa Otona Gal

Yuusuke Taguchi, a third-year high school student, passed his university entrance exams on a recommendation and thus had some free time. Then, his homeroom teacher asked him to be a tutor for "a certain woman who is aiming to get into university," but waiting for Yuusuke was Airi, a gal six years older than him. Moreover, Airi is kind and easygoing, but... it seems she has an even more outrageous "secret"?

(Source: Akita Shoten, translated)