Yuji visits his future mother-in-law, Yumi, at her home to formally ask for her daughter's hand in marriage and is warmly accepted, leading to their marriage. Since Yumi's husband has already passed away, she feels lonely after her daughter moves out. Yuji and his wife decide to live with Yumi at her family home. Six months pass, and Yumi grows increasingly tormented by the sounds of the couple's nightly intimacy, resorting to masturbation to cope. Reaching her breaking point, she sneaks into Yuji's bedroom one night while her daughter is away, determined to forge a forbidden relationship with him.