Which studio partnered with Game Freak to co-develop Pokémon Pokopia?

Omega Force partnered with Game Freak to co-develop Pokémon Pokopia.

Omega Force is a studio within Koei Tecmo, and it joined the project because of its experience with sandbox-style game design. Game Freak, the longtime Pokémon developer, had less experience making this kind of open-ended building and simulation game.

The collaboration brought together Game Freak's Pokémon expertise and Omega Force's experience with construction-focused environments. The game's development was also influenced by Dragon Quest Builders 2, a previous sandbox title associated with Omega Force's experience.

The arrangement does not mean Omega Force replaced Game Freak. Game Freak remained a co-developer, while Koei Tecmo's Omega Force worked alongside it. Nintendo and The Pokémon Company are listed as publishers, which is another role separate from development.