The eponymous 4-5 year old main protagonist who moves into a ramshackle apartment building and becomes a next-door neighbor to manga artist Shin Karino; he also enrolls himself into a local kindergarten called Shimizu Kindergarten, where he is in the Star Class. Having the mental capacity of a mature adult, Kotaro is very independent for his age; Kotaro often carries around a plastic toy sword that he keeps around his hip, and acts like a samurai due to the love of his favorite cartoon Tonosaman.
Over the course of the series, it is implied that Kotaro was neglected and abused by his parents to the point where Kotaro resorted to eating tissues. At some point, Kotaro's mother abandoned him and his father, and later died from an unknown cause; he then left his father's custody and sent himself to go live at a
foster facility.
