In'youchuu Etsu Kairaku Henka Taimaroku by TinkerBell - Adult Sex Game

One day, Yamato, Mikoto and Takeru visit a village in the mountain for the training to be monster hunters. They have various hard trainings and finally become the monster hunters. But there is something wrong with Yamato's body.... His body gradually changes into a monster.... What is happening to his body? Who can stop it? To save Yamato, Mikoto and Takeru make every effort. What is a secret of Yamato's body? What will happen to Mikoto and Takeru?