In the Miyagawa household, 11-year-old Atsushi appears as an adult, while his 17-year-old sister, Atsumi, is pint-sized. Amid Atsushi's mistaken arrests and Atsumi's perpetual childlike interactions, their lives brim with chaos. Adding to the mix, Atsushi unwittingly captures the affection of Atsumi's schoolmate, who remains unaware of his real age. This quirky family never lacks excitement or surprises.