The Hisui region (Japanese: ヒスイ地方Hisui region) refers to Sinnoh as it was known during discovery and settlement, in a historical period set prior to Generation IV. It is the setting of Pokémon Legends: Arceus.
Hisui is likely based on the Japanese island of Hokkaido while it was still known as Ezo, referring to its inhabitants prior to the Meiji Restoration. In 1869, the northern frontier was renamed to its current administrative title, which translates to northern sea circuit.
According to Cogita who is their descendant, the earliest human inhabitants of Hisui lived one or two millennia before the events of Pokémon Legends: Arceus. This society worshiped Arceus and built the ancient ruins that can be found across Hisui and modern-day Sinnoh, such as the Solaceon Ruins and Snowpoint Temple. There is a legend of an ancient hero who worked together with the ten Noble Pokémon gathered the Plates to find Arceus.
The next humans to arrive in Hisui came from across the sea. The Diamond Clan and Pearl Clan both worshiped a deity known as "almighty Sinnoh", with the Diamond Clan claiming it created time and the Pearl Clan claiming it created space. This disagreement led to fighting between the two clans. During the time that the Diamond and Pearl Clans lived in Hisui, the Galaxy Expedition Team comprised of people from many regions came to Hisui to settle it, introducing the natives to new concepts such as Poké Balls.
