https://www.dlsite.com/books/work/=/product_id/BJ01053135.html
As always, please support the artist and buy his works.

Boom! A school-approved harem reverse rape at a young lady's school full of bitchy students!

A new teacher, Yu Haine, is assigned to Seimei Jogakuen, a long-established private girls' school where only true-born young ladies are allowed to enroll. He quickly becomes loved and admired by the students, who call him ``Yu-chan.''
However, the students at this school have too short skirts to be called young ladies, and they keep flashing flashes of their chests, making them seem too close to men.
Yuu is entrusted with student guidance, and he finds himself alone with one of the students, Rika, in the student guidance room.
Rika, who acts as if she is used to dealing with men, begins to seduce Yu in his ear...!