Take it back to the very beginning. The day that Ash (Satoshi) oversleeps and ends up with a testy Pikachu. Then tell the backstory of how the world came to know the existence of Pokémon, and why they are important to mankind’s survival. This story doesn’t have to be the canon of the game. Take Ash (Satoshi) to the point where Pikachu trusts him and saves him, then it can cut to your trainer and you can follow your own adventure–woven into the fabric of the original tale–as you gather and train your own Pokémon.