Eternatus came from a planet where Pokémon could naturally Dyna/Giganta/Eternamax, possibly due to evolving alongside exposure to exotic energy and matter in another region of space. Eventually the planet was destroyed due to the massive destruction caused by all the giant battles. Eternatus was blown into space, trapped in a piece of its planet, until it crash landed in Galar 20,000 years ago, wiping out the local Corsola and Dreepy lines. Pieces of debris from the chunk of planet peppered the Galarian landscape and created the strange hexagonal stones in the Max Raid Dens while pieces of Eternatus' body got caught in the planet's orbit, gaining a trajectory that eventually has them rain down in Galar as Wishing Stars and Wishing Pieces. Eternatus lay dormant until 3000 years ago, the same time period where AZ fired the Ultimate Weapon at Galar, possibly reanimating Eternatus and causing the Darkest Day.