The series involves the exploits of the Phantom Thief Tonchinkan, in reality an alias of four different individuals with fighting abilities, Kung-fu master Tonpu, mechanic Chinpei, and psychic Kanko, alongside their nonsensical junior high teacher Nukesaku.

The manga initially began as a parody of the Phantom Thief genre, with each of the four issuing calling cards stating Tonchinkan's intention to steal a certain worthless object.

As the series progressed, the thievery element was toned down in favor of slice-of-life school-based gag comedy, usually revolving around the three students and their teacher encountering something odd or destructive at Reinbou Junior High.

Endo himself was aware of this theme change, and poked fun at how often the plot would switch with a gag in a chapter of a caricature of his editor poking out stating "Thievery stories two weeks in a row..."[1] Tonchinkan began as a two-chapter miniseries in Fresh Jump taking the place of Endo's then-currently transferring series Shinigami-kun, which was moving to Monthly Shōnen Jump.

Later on, he had figured out the concept of a phantom thief series after watching television, alongside the news that Cat's Eye was soon to end its run in Weekly Shōnen Jump.