18+ Sei Shoujo: Seido Ikusei Gakuen

Tokisawa Naomi, currently unemployed, is a worthless drunk who can't even pay for his drinking bill of the day before.

Luckily he has a job offer to be a teacher from a prestigious high-school. While Naomi indeed has a degree in teaching music that's not why he is offered the job, at all.

Tokisawa Naomi is a renowned pimp and trainer of prostitutes. Though he doesn't simply break the girls; Naomi awakens their secret desires so that they are selling their bodies willingly.

The high-school doubles as a modern place to train prostitutes for the country's upper class.
Naomi's has to train five students. He accepts but only under the condition that he is free to choose the girls.

(Source: VNDB)