Aika, a mother who lost her husband in a traffic accident three years ago, has been raising her only son, Yu, while taking care of her father-in-law, who has no other relatives. Yu, who has always seen her mother working hard despite being busy with daily life, secretly wants to become independent and repay her parents. One day, Yu sees her father-in-law, who is supposed to be sick and bedridden, groping Aika's body with lewd hands as he devotedly takes care of her.