Soukan Yuugi  

  相姦遊戯

Yuji is given a board game by a salesperson, "People who play this game together can get along well." This is not an ordinary board game. Yuji plays it with his mother and sister.... Once they start it, they cant go out of the room. In the confined room, they keep throwing the dice. And they are forced to do erotic actions by following missions....