A man accidentally gets alone with his wife's mom friend during a mixed bath at a hot spring inn. The man who gets an erection while thinking it's not good, masturbates to avoid being noticed, but is found out. However, a mom friend wants to see her masturbate, perhaps because she felt happy to be seen as a sexual object. Then, seeing the raw cock and the man getting excited, he felt a bit heavier, and he couldn't hold it in and reached for his cock...