The ChuChus are the titular characters as well as the main protagonists of the action puzzle game ChuChu Rocket!!. They are space mices who build and pilot rockets to save their lives from the space cats KapuKapus. The ChuChus have appeared in several crossovers with NiGHTS.
The Nightopians made a guest appearance in the ChuChu Rocket! game as an unlockable skin for the ChuChus along with the Chaos from the Sonic the Hedgehog series. To unlock both skins, the player must beat all of the 50 courses from the game.
Sonic Pinball Party
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The ChuChus appear in Sega Superstars, in a ChuChu Rocket!! thematic mini game. The player must keep their hands over the buttons to make bridges appear so the ChuChus can reach their rockets. The player must also release their hands from the buttons to deactivate the bridges when the KapuKapus appear.
Sega Superstars Tennis
The ChuChus appear in the ChuChu Rocket!! thematic mini game, which takes place in the Space Channel 5 tennis court. In the mini game, the player must guide the ChuChus to their rockets by shooting the tennis ball at the arrow panels which make the ChuChus go to the direction the arrow is pointing.
Sonic & All-Stars Racing Transformed
The ChuChus make a cameo as a hologram in the Race of Ages circuit.