Play as the child Cody, whose grandpa has just retired and is leaving him with the family business, a Robopon Dispatching Company. The player starts with one Robopon, named Sunny, and must travel Porombo island as he/she collects Robopon and uses them to battle other Robopon Collectors. The collectors primarily played against are known as the "Legend 7", who are the top-ranked collectors of Robopon on the island. When Cody beats a Legend 7 member, he takes their rank.

To improve Robopon, they must be upgraded by adding software or other parts to them. Each part has a certain amount of space for storing software and will determine what attacks can be used by the Robopon. Software can be mixed to generate special attacks.

Ultimately, Robopon plays a lot like Pokémon. Fighting is turn based and is between two Robopon owners who tell their Robopon to issue attacks or go on the defensive. Robopon can be healed in mid-battle with spells (which can be bought in town shops or stumbled upon between towns) or taken to a Robopon dispatch center and healed in their machine. One thing where Robopron differs from Pokémon is that in battle, a defeated Robopon sometimes will drop add-on items which get claimed by the winner. When a new game is started, the game asks for the player's birth date which is actually used by the game to select the first Robopon the player will start with.

In Japan, Sun Version was released alongside Star Version and can connect to that version via infrared sensor. There are 153 different kinds of Robopon, and only by trading between versions can all of them be collected in one save.