>>2729491I dont use nhentai so i don't know the links there but here are a couple doujinshi titles:
Hokentaiiku Gakushuu Note
Futo-chan no! Hokentaiiku de Kikiippatsu!?
There is also some image set by the artist orangebullet (also known as hanainu) with "sex education" like this. Loli warning for his art though.
The japanese word of note for your searches would be 保健体育 hokentaiiku (Health and physical education). 授業 jugyou (lesson) might also come up with some things if paired with an embarassed/humiliation tag wherever you're looking.
