Intou Joubo ~Yukemuri ni Ukabu Bibo no Karada

Because Hiroki's father died, his mother, Shiori, has raised him alone. To repay her, Hiroki has taken her to a hot spring for a vacation. Secretly, Hiroki loves his mother as a woman. When she gets drunk and suggests they bathe together, it starts a fire in Hiroki that won't calm down...