Four-year-old Kotarou Satou lives entirely on his own in a Tokyo apartment building, cooking, cleaning, and paying rent with no adult in sight. His neighbors, struggling manga artist Shin Karino and pub hostess Mizuki Akitomo, can't quite believe it and start looking out for him, only to find the boy quietly looking out for them instead. Told in self-contained chapters, the series follows Kotarou's daily routines and the found family forming around an apartment building that doesn't ask too many questions.