The 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.