Azusa takes refuge at her sister Reiko's home to protect her son Naoto from her husband's abuse. Reiko warmly welcomes them, but secretly harbors strong sexual desires toward Naoto. Meanwhile, Azusa, feeling liberated, indulges in masturbation in the bath, only to be caught and assaulted by Reiko's son, Shou. To ease the ensuing tension, the two begin drinking and eventually give in to passion. As their sons uncomfortably leave the room, their forbidden relationship deepens, bringing unexpected events and emotional turmoil that ripple through the household.