On the surface, Miyagawa Atsushi (voiced by Okiayu Ryotaro) is a mature man of 1.8 meters tall, but in fact, he is only a 12-year-old boy. He is surprisingly popular among girls because of his height, but he also has a lot of troubles. Atsushi Miyagawa's older sister, Atsumi Miyagawa (voiced by Rie Kugimiya) is currently in the second grade of high school, but she, who is super petite at 1.37 meters, is often mistaken for Atsushi's younger sister.
God made a little joke, but the upside-down two people lived hard in trouble and trouble. Saya, who likes Atsushi (voiced by Aya Hirano), and Futami Moriyama, who cares about Atsushi (voiced by Tomoe Tamiya), has been accompanied by Atsushi’s friends, Xiaogreen (voiced by Nami Kashiwayama) and Xiaojun (voiced by Sakiyako Tojo), Every kind and innocent people are silently helping both siblings in their own special ways.