Adult PC Game: Shinseki no Obasan ~Hanare no Netsujo, Honke no Gosai~ by Guilty+ Archive

Main character returns to his home village. At night he goes to the sound of water in the woods behind the house and sees his mother masturbating in the basin. She accepts son's desire, and their secret meetings start to happen at various places in the village.

Shinseki no Obasan ~Hanare no Netsujo, Honke no Gosai~ by Guilty+ Gameplay Preview