Moekoi Ishin! ~Atashira, JK, Shinsengumi!~

Tsubasa is normal in every single way, except that his family left him in severe debt, so he is constantly doing part-time jobs. However, his luck changes when he becomes the fiancé of a girl from a famous family due to a promise by his late grandfather. If he accepts the marriage, the debt will be paid off for him. He ends up transferring into Gose Gakuen where the head of this household was the schoolmaster. The girl he is to marry, Kurumi, is a cute, proper and prim ojousama who is guarded closely by a group of girls. They declare that they will not allow him to marry her until they deem him worthy to be her fiancé. To this end, they train him to be a great man in all ways, including in bed.

[From Hau~ Omochikaeri!]