Since the story of Pokémon Legends: Arceus takes place in the Hisui region, which later becomes known as the Sinnoh region, the game pays homage to Pokémon Diamond and Pearl through various Easter eggs and references. One of them is presented near the end of the players' journey when they have to choose between the Diamond and the Pearl clan.
Source:https://www.cbr.com/pokemon-legends-arceus-diamond-pearl-clan-choice/