A hot spring trip for just the two of them with the son they raised alone. When they first soak in the hot springs together, the son sees his mother's body, which is still firm, and he can't help but lust after her. When her son asks for sex, she initially refuses, but being young and still with a strong libido, she gives in to his demands. The forbidden door has finally been opened. The desires of mother and son reach their peak.