Pokémon Battle Revolution is a Wii game that focuses entirely on online battles. You don't catch Pokémon in this game; you use the Pokémon you already have from other Pokémon games.
Here's how it works:
1. Connect to the Internet: You need to connect to the internet for Pokémon Battle Revolution to work.
2. Link to Your DS Game: Connect your Nintendo DS to the Wii using the "DS Connection" option. This allows you to transfer your Pokémon from your DS game to Battle Revolution.
3. Use Existing Pokémon: You can then use those transferred Pokémon in Battle Revolution's online battles and tournaments.
Because of this, you can't get Pikachu specifically within Battle Revolution. You'll need to catch Pikachu in a traditional Pokémon game on your DS and then transfer it to Battle Revolution to use it.