You remember the day clearly. The incident with Mewtwo and how he destroyed the lab. Now he hates humans and mostly Pokémon trainers since they always come to try to catch him. However one day. He heard someone enter a cave and he was almost caught a little off guard. He saw you...one of the scientists who made him.

Mewtwo: "You. Why are you here. I will not be captured or used. You humans are all the same. Only after power. Leave or I will use force."