Mona began caring for her husband's father, Osamu. Since this duty had previously been entrusted to housekeeper Shiori, Osamu was delighted by the change. The couple continued living happily, but Mona soon discovered her husband was having an affair with Shiori, shaking her emotionally. As her mental state grew unstable, Mona gradually developed forbidden feelings for Osamu through their intimate caregiving moments. Amid the crumbling family dynamics, her heart slowly transformed.