The Mewtwo uses its psychic powers to lift you up to its face. As you're raised up, you see that it is male from the organ between its legs. You blush and look away quickly. The Mewtwo doesn't notice and examines your tiny form "Hm...appears to be a tiny human, but how?" You're terrified of the Mewtwo, he's big enough to do anything to you.
The Mewtwo pets your head lightly and you cower a bit. The Mewtwo says through ESP "Do not fear, I don't want to hurt you, some other Pokemon might want to though, and I wish to protect you." You look at the Mewtwo, you're less scared now since the Mewtwo says he is going to protect you. He tries to smile and continues speaking "I have the perfect way to protect you too: I'm going to let you live inside of me"
You blink and say timidly "But...won't your insides hurt me?"
The Mewtwo shakes his head "I said let you live inside me, meaning you won't be harmed. You'll live inside me, protected, warm, and well-fed." You think for a while, it would be interesting to live inside a Pokemon, especially a legendary like Mewtwo. The Mewtwo opens his huge mouth and you look inside. His warm breath washes over you, and it doesn't smell too bad, it's actually quite soothing, "Ready to come inside, human?"
You nod and you see the tongue getting closer. The Mewtwo sticks its tongue out and drops you onto it. You land on your rear on the squishy surface and he brings his tongue back in and closes his mouth, leaving you in the dark. You trust the Mewtwo to not hurt you.
You feel yourself slide down and hear a gulp, which brings you into the throat. You stay still and can hear a murr coming from the Mewtwo, he seems to enjoy having you go down your throat. You kind of enjoy being dragged down, the throat muscles feel as though they are massaging you. Soon, the throat opens up and you freefall into the stomach. There is no acid, which meant the Mewtwo was telling the truth.
He sits down against a tree "My body is your new home, you may go anywhere inside me." You look around, the stomach lit up with a faint light so you can see. You see two chambers, the right one seems to lead to his intestines, and the one on the left leads to other chamber that could be anything.