Rin is a family of three with her husband and her stepchild Akira. However, recently her husband has been busy with work and not at home, so Rin and Akira have been spending their time alone. One day, when Akira was about to take a bath as usual, Rin was already there. And without realizing that Akira was watching, Rin started playing with her crotch and masturbating.