As I am getting a Battle Tower team ready, in Pokémon Pearl I do not have my starter pokémon with me. I would love to, but since some of my Battle Tower pokémon are strong enough to battle pokémon in the grass by themselves, I don't need it. Perhaps if I had my starter for the Battle Tower, I would be able to keep it with me, but since I chose not to it is in the PC. Though it will come back once I reach a certain amount of Battle Points at the Battle Tower.