Before he can get to Pastoria City, Ash has to battle a slang-talking Trainer named Sho. Sho wants to collect a Pikachu evolution set and he already has Raichu and Pichu, so he has his eye on Ash's Pikachu—but Ash isn't about to trade. Instead, they have a battle: Sho's Raichu vs. Ash's Pikachu. Raichu isn't afraid to go head-to-head with Pikachu, and it also knows Hyper Beam, a move that Pikachu can't learn unless it evolves. Not only does Raichu beat Pikachu, Paul drops by just long enough to sneer at Ash for not having evolved his Pikachu.
While Pikachu gets some serious rest and recuperation at the nearest Pokémon Center, Ash takes out the Thunderstone he received in Vermilion City. Back at the Vermilion Gym, Lt. Surge's Raichu beat Pikachu and forced it to consider whether it wanted to evolve; even though Pikachu decided to remain a Pikachu, what if it's changed its mind since then? Team Rocket saw the whole thing unfold and they still think Pikachu should stay the same, so they swipe the Thunderstone when no one is looking.
It's just as well, since Pikachu decides to beat Raichu itself. After some special training, it's time for a rematch. Instead of relying on raw power, Ash has Pikachu use strategic moves and spinning tricks to beat Raichu. Sho admits that Ash's Pikachu is pretty good—but if they ever meet again, the result will be different!