Omega Force’s sandbox experience helped inspire Pokémon Pokopia’s development partnership.
The game was conceived by Shigeru Ohmori, who believed players would enjoy cultivating their own Pokémon habitats. Because Pokopia required extensive building and sandbox design, Game Freak partnered with Omega Force, a Koei Tecmo team with relevant experience in that area.
The partnership was particularly associated with Omega Force’s work on Dragon Quest Builders 2. That experience made the studio a natural collaborator for a Pokémon game centered on constructing homes, reshaping terrain, gathering materials, and developing communities rather than focusing mainly on combat.
Game Freak remained a co-developer and supplied deep Pokémon expertise, so it is easy to answer Game Freak when thinking about who made the game. However, the question asks which developer’s sandbox background influenced the partnership. That specific answer is Omega Force.