Based on the erotic game by Lilith Soft.

"Mana supply is a holy deed, so we're not embarrassed!"

At Witch School, girls are trained to produce the best "mana supply" (sperm).
Sex is no mere leisure activity, nor is it a brutal affair.
Students are arranged in boy-girl pairs to ensure a constant supply.
Mana enhances a Witch's powers so she can battle the Eaters!
It's in everyone's interest that everyone master all kinds of sex technique.
More pleasure, better mana. Better mana, stronger Witch!

* Boys supply the mana, girls absorb it; everyone is a pair.
Will you choose Rina or Alyssa? While living school life choices will arise
which affect sex scenes and the ultimate route with one heroine or the other.
Do well and you'll get a happy end. But with who? That choice is yours.

(Source: DLsite English)