The Pokémon Legends: Arceus has garnered a lot of attention for its novel setting, offering a look at the past eras of the technologically-advanced Pokémon world. The most dedicated fans, however, might a trip even further into the past where the series' titular creatures were used to wage war.
The Nintendo DS strategy game Pokémon Conquest, a crossover between Pokémon and the Nobunaga's Ambition series, was a 2012 game set during the Feudal era in an area called the Ransei region. It was accompanied by a manga release, known as the Ransei Color Picture Scrolls, with different chapters themed after different colors, each of which follows a character from the game as they go through life in this past era. The time in which the game is set predates the existence of even steam-powered Poké balls, so Pokémon work together with humans only after developing strong bonds--meaning most people are lucky to have even one Pokémon.
In the first chapter, the White Scroll, a young girl named Oichi and her Jigglypuff become lost in the woods, and are put in serious danger when a horde of wild Pokémon attack. The second chapter, the Green Scroll, depicts early Pokémon battles and their use in warfare: armies would send champions out to perform individual battles alongside their Pokémon, and the winner's side would be declared victorious. Champion battles are often accompanied by massive feasts to celebrate victory. Many of the characters in Ransei are also depicted with armor and even weapons like spirit sutras and clubs, implying some conventional warfare alongside the Pokémon battles. Without Pokémon centers, traditional medicines and salves are the only options for healing. Pokémon are also shown helping out with everyday tasks, such as farming and harvesting. There are six chapters total: White, green, yellow, scarlet, blue, and black.
While many Pokémon spin-offs are of dubious canonicity, Ransei Color Scrolls and Pokémon Conquest do have some interesting connections to what's been revealed about Pokémon Legends: Arceus. In preview trailers, at least one character has stated that she didn't need Poké Balls, and controlled her partner through their bond. The biggest connection is that both games treat Arceus as extremely important: the Ransei region is shaped in Arceus' image, while Arceus is said to be responsible for the birth of the Sinnoh region (and presumably the transformation of Pokémon Legends: Arceus' Hisui region into Sinnoh). Ransei is also split into several kingdoms, each aligned with certain Pokémon types (excluding the Fairy type, which didn't exist yet), similar to the way that Hisui appears to be broken up into bounded sandbox areas. One of the key plot points in Conquest also deals with Nobunaga's desire to strike down Arceus and prove himself superior to the godly being--something that's been highly speculated in Pokémon Legends: Arceus, since the original Sinnoh region plot similarly revolved around taking the powers of these god-like creatures to restart the world according to the villains' wishes.
While direct connections between Ransei and Hisui are unlikely, the Ransei Color Picture Scrolls do provide a look at what The Pokémon Company thought the past of the Pokémon world should look like, at least at one point: a time before Poké balls, when friendship and cooperation between trainer and Pokémon was more important than ever.
