After a specific incident, Tetsuji quit playing baseball and has been wasting his high school years ever since. However, everything changes when his elder sister, who is now married, returns home by surprise. Tetsuji, who stands at a massive 188cm, is too apprehensive to ask about his sister's weight. Mao, his sister, is known for her towering presence and is nicknamed "Demon King," in stark contrast to her reserved and also plump brother. The two siblings unexpectedly embark on a poignant and gratifying summer holiday.
