25-sai no Joshikousei: Kodomo ni wa Oshierarenai Koto Shiteyaru yo

It's Kaho Miyoshi's first day back at school, and she can't wait to get started. However, "Kaho" isn't a high school girl: her name is actually Hana Natori, and she is 25 years old! Because the real Kaho was on the verge of being kicked out due to her regular absences, Hana promised to fill in for her since the two of them look alike. However, that's easier said than done when Hana can't even relate to high school kids anymore.

When Hana makes an excuse to go to the nurse's office, she is accosted by an acquaintance of Kaho, who wants her to show him a good time. But before things can escalate, she is saved by Okito Kanie, a teacher and a former classmate of Hana's. Okito immediately recognizes Hana and wants her to give up her charade. When Hana refuses, Okito makes it clear that she will have to "buy" his silence with her body.