According to Ōshū mythology, there are three great forces in the world held in a state of fragile balance: The forces of sky, sea, and land, represented by three incredibly powerful Pokémon. Each creature was said to live in the most inhospitable of environments, from the deepest oceanic trenches, to the highest reaches of the sky, to the deepest and most wild regions of the continent's wilderness. It was this very nature, this association with the unreachable and dangerous edges of the world, that earned the three legendary beasts their title: The Extremis Trio, nigh-divine beasts of incredible power.

The oldest and most dangerous of the three is the deep sea beast known as Abyddon. Titanic in size, Abyddon dwarfs even Wailord in mass. Spoken of in hushed tones by mariners, it's believed that Abyddon is directly responsible for the sinking of countless ships, and the devastation of coastal communities during fits of primordial rage. It's said that many great storms that have swept the seas and shores of the world come from the thrashing, armored body and blade-like fins of the ferocious Extremis Pokémon as it rails against the world.

Known to appear more frequently in the icy waters off of Opoc, Abyddon is a ferocious hunter and an indiscriminate predator with little concern for much beyond eating and proving itself to be the dominant force in the sea. The only thing that ever truly seems to enrage the deep-dweller is when the skybound Whelkin descends into the lower atmosphere to feed. It's theorized that Whelkin's powerful, ambient electrical field disrupts Abyddon's senses, driving it into a fury.

The only force in the world that's said to be able to keep the peace between the two is the third Extremis beast, Firmastodon. Any time Whelkin and Abyddon prepare to do battle, Firmastodon awakens and thunders across the continent to interrupt their battle. In those times when Firmastodon has been too slow, or too far away, the results have been catastrophic, nigh unto apocalyptic, for everything within range of the warring beasts.

To even dream of challenging Abyddon is foolhardy, but nobody ever said your average Pokémon trainer had a wealth of intelligence when it came to the fights they pick.

Abyddon, the Primordial Sea Pokémon, No. 01 in the Ōshū Legendarium.

Art by the always awesome  Goatmystic