25-sai no Joshikousei
Genres: Romance, Hentai
Type: ONA, Episodes: 12
Aired: Jan 8, 2018 to Mar 26, 2018
Studio: Lilix
Source: Web manga
Rating: Rx - Hentai
Synopsis:
Once most students are done with high school, they leave and never come back. However, at 25 years old, Hana Natori  finds herself in the role of a student once more at her aunt's request. 

Since Hana's cousin, Kaho Miyoshi, refuses to go to school, her aunt begs Hana to take Kaho's place, since the two of them are practically identical. But as luck would have it, she is recognized by Okito Kanie—an old classmate from her days in high school—who is now a teacher! With her cover blown, Hana assumes Kanie will expose her secret. But when he suddenly kisses her, she soon learns he has other ideas.