Because the way people have a high interest in "sex," a sex school was formed in order to fulfill the students' desires and help them become more advanced in their skills.

One of the story lines....
Ion, in order to help pay off the debts in his family, has enrolled in the school, hoping to gain knowledge and sell out his body in the future to gain money. But Ion gains more than just "knowledge" in the sex industry, and he starts to fall for his Instructor Asagi...but love is strictly banned from the school...