Raichu is the evolved form of Pikachu. There's no further evolution for Raichu in the mainline Pokémon games.
Here's the evolution chain:
* Pichu evolves into Pikachu at level 15.
* Pikachu evolves into Raichu by using a Thunder Stone.
If you're curious about other evolution methods in Pokémon, let me know! 😊