A lewd filial piety for the son: shoulder tapping ticket to loosen the stiffness of mother and child

One day, his son Hiro, who is in puberty, accidentally peers at his parents' sex. Hiro is even more shocked to see such a thing as her parents, but she is shocked that she wants to do it with her mother, Reika. Since then, Hiro keeps his distance from Reika like he is in a rebellious phase, but the "helping ticket" that Hiro gave Reika when he was a child brings the mother and child closer again. And then, filial piety, expressing gratitude to my mother, gradually transforms into lewd filial piety...