Made in response to Seras4797's challenge (as well as with some inspiration with the person's own stories), using the Legendary Pokémon Deoxys...in Fire Emblem: Awakening...

Prologue: The Space-Faring Adventurer

Jar'kai was one of many in a race known as Deoxys, noted for their ability to shift their DNA into any form they wish, and their powerful psychic powers. Technically aliens to the Pokémon world, Deoxys had come from space, where they were created due to a virus reacting to encountered DNA.

Now, one of these alien Pokémon were flying through the outer reaches of space, exploring. Jar'kai, given this nickname by a human Trainer that befriended him, was an adventurer among his people, constantly going to new systems and exploring, sometimes returning to the home his people had chosen to inhabit, a world called by its inhabitants as the 'Pokémon World', or as the Deoxys called it, 'the World of Origin', due to the progenitor of life in the galaxy calling the Pokémon World home.

However, as Jar'kai drifted through space, he came across something...abnormal. As he approached, he saw...a tear...in the fabric of space and time. 'Palkia and Dialga would be pissed if they saw this,' Jar'kai thought to himself. He observed the phenomenon...and it began to expand. It took Jar'kai some time to realize, 'By Arceus, it's expanding towards ME!' Jar'kai turned to flee, but the rift overtook him.

In a nearby star system, Jar'kai's 'sister', Tulinaya, nicknamed such by the same Trainer that named her brother, sensed her 'brother's' disappearance. Feeling for where he was at the time, she shot straight there, unaware of where Jar'kai was, or what adventure he was getting himself into on the other side of the rift...

Well, here's my Seras4797-style generic prologue, in case I get inspiration for additional such stories...lol...