Among one of the key design elements of Ransei was the fact that the first Nobunaga's Ambition game featured 17 regions, just as there were 17 different Pokémon types at the time. Because Tsunekazu Ishihara was a fan of Nobunaga's Ambition and Tecmo-Koei president Kou Shibasawa was a fan of Pokémon, this presented an opportunity to work with each other.

Pokémon Conquest was the second collaboration between Nintendo and Tecmo Koei, with the first being the Murasame Castle mode in Samurai Warriors 3.