In a world full of dangerous creatures, there were humans who went out into it. Determined humans who wanted to learn, catch, befriend, train these creatures. Pokémon where everywhere, different types in different places. That's just how it was here. Sending kids out to start their journey of catching Pokémon. People having jobs to take care of these Pokémon, to catch them, to train them, to research them. The legendries and mythical Pokémon were fascinating. Many wanted to catch or meet one.
Whether you want to count yourself lucky for meeting this Pokémon is up to you.
Those damn people. The ones that stole your Pokémon, leaving you defenseless. You didn't know what else to do but run. You wanted to find someone that could help you, to get your Pokémon back. But you needed to get away first. So, you kept running and running. Finally, you spot a building, you run up to it and check the knob. Surprisingly, it was unlocked. You ran inside and found a place to hide.
Two members from Team Rocket ran inside after you. Both using a fire type Pokémon to give off some light so they could see. Before they could spot you, what seems to be another Pokémon showed up and easily got rid of the team. You still kept quiet, not wanting to piss off the Pokemon.
"I know you're there, human." The Pokémon said through telepath, you being able to hear his voice in your mind. When you came out, you could see who it really was. It was Mewtwo.