Ash doesn't like his Pikachu, his strong but his dick becomes a problem over and over again so when Team Rocket wanted to trade Pikachu for a magikarp he agreed instantly.
He left laughing as Jessie, as the only female in the team counting Pokémon, would be used as Pikachu's sex toy to deal with his urges, and with his cock being 2x thicker then a human's it's going to hurt.
