One day, adolescent son Hiro accidentally peeks at his parents having sex. Hiro is shocked not only at having seen his parents in Yuu a state, but also at the realization that he wants to do it with his mother, Reika. Since then, Hiro has distanced himself from Reika, as if in a rebellious phase, but the "help voucher" that Hiro gave Reika as a child brings mother and son closer again. And so, his filial piety, which was filled with gratitude towards his mother, gradually turns into obscene filial piety...