Gorochu was the name of Pikachu’s abandoned planned final evolution.
In the original development plans, Pikachu evolved into Raichu, and Raichu was intended to evolve once more into Gorochu. Gorochu was described as having large fangs and two horns, giving the evolutionary line a stronger and more formidable final stage.
The character was removed before Pokémon Red and Green were completed. Cartridge-space limitations were a major challenge during development, and several planned Pokémon or evolutionary concepts were cut. Gorochu therefore never appeared as an obtainable species in an official game.
Pichu was added later as Pikachu’s pre-evolution in Pokémon Gold and Silver, completing a different three-stage structure: Pichu, Pikachu, and Raichu. That later addition is why fans sometimes assume Raichu always had only one evolutionary relationship on both sides.