Deep Fantasy

Island Seasus stays with the southern part cursed and northern part shredded by the dragon.
Southern part grew and developed while north drowned in conflict and ruin. Rulers of the South searched for a maiden to lift the curse and managed to take two royal blood princesses captive during the first war. But the ritual is going to fail unless princesses cooperate, and to ensure that main character is giving them sexual training.

[From vndbreview]