After divorcing her husband, Izumi has been raising her only son, Takeo. They are a typical "single parent household," but Takeo is not rebellious and is growing up healthily. Then, one day, Takeo goes abroad to study for three weeks. He leaves Izumi in the care of his best friend, Masahiko... Then, while Izumi is away, an incident occurs at the Takashima household. Izumi's ex-husband appears in front of Izumi and becomes violent. Masahiko happens to be there and ends up helping Izumi, but...