Miho returns to her hometown with her husband to attend her stepmother-in-law's first memorial service. Upon arrival, she notices her father-in-law looking weary and lonely, though he puts on a strong front in front of the couple. His quiet resilience contrasts with her husband's urban demeanor, stirring something deep within her. One evening, her husband suggests setting off fireworks to lift everyone's spirits. The father-in-law wears his late wife's yukata, and as he gazes at the fireworks, the resemblance overwhelms Miho. Overcome with emotion, he suddenly collapses into her arms, weeping. That moment of vulnerability ignites an uncontrollable passion between them, leading to intercourse filled with the weight of his lost love. Though tormented by guilt toward her husband, Miho resolves to indulge in this forbidden relationship for just one week. Deep down, she can no longer resist the ache of her father-in-law's loneliness—and surrenders completely to their illicit bond.