The leading characters of Mittsume ga Tooru are almost all members of Tezuka's acclaimed Star System - that is, they appear in other works besides their own.

Tezuka himself is a Star System character and appears in the anime as Sharaku's classmate, Osamu.

Sharaku has made minor or major appearances in Black Jack, Astro Boy, Buddha, Rainbow Parakeet, Marine Express, One Million Year Trip: Bandar Book, This is What's Going to Happen in 1983 and The Last Mystery of the 20th Century, as well as in the Astro Boy: Omega Factor Game Boy Advance game and the Black Jack Nintendo DS game.

Generally speaking, Sharaku's other appearances are confined to either his docile or his Three-Eyed personality, but an episode of the 2003 Black Jack anime (where shy Sharaku is a recurring character) features the Red Condor, an "evil" Sharaku - including vest draped around his shoulders like a cape - and other references to the series. Other allusions in this show are made to Sharaku's other personality, though they appear to simply pay homage to Mittsume ga Tooru rather than truly confirm what's under the bandage. His first name in this series is also 'Sharaku' rather than 'Housuke'. Dr. Kenmochi once again plays Sharaku's father.

Wato also makes appearances in other stories (inclding the aforementioned Black Jack anime, as Sharaku's sister, a kendo captain who is petrified of snakes), and Higeoyagi, as one of Tezuka's original and most famous Star System "actors," has appeared in dozens of roles.