Master & Slave ~Goshujin-sama to Mesu Dorei~

In medieval world people start studying magic. In remote forests of a kingdom there is an educational facility for girls practicing magic. Main character holds a laboratory there, but he has a reputation of a sadist, so students avoid it. This year there are four girls who enroll to the laboratory. It becomes a great surprise for protagonist. Well, now time's for fun.

[From vndbreview]