Japan's Patent Office has rejected a patent that Nintendo filed describing the mechanics for capturing creatures in games—the fundamental system at the heart of the Pokémon franchise. In its rejection, the Office referenced an unofficial, decade-old fan recreation of Pokémon gameplay as evidence that such a system was already documented prior to Nintendo's filing, finding little reason to regard it as a novel inventive step.

The decision has triggered a dispute between Nintendo and the Patent Office, with the company arguing that it was inappropriate for the Office to base its rejection on a copyright-infringing fan game. Patent professionals have noted that the Office's response contained language and tone that departs significantly from typical patent office communications, suggesting an unusually critical stance on what Nintendo claims should be protectable intellectual property.