Her daughter is cheating on her husband. When her stepson comes to her for advice, Nariko can't help but feel responsible. Her daughter's infidelity is due to her inherited infidelity. And because of it, her stepson is deeply hurt. Nariko is filled with remorse and, as an apology, she pulls down her stepson's pants and reaches for his penis. She makes him feel good on behalf of her daughter. That was Nariko's way of apologizing.