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In Pokemon Diamond and Pokemon Emerald if you choose to play as a boy the girl becomes a supporting character. Does the same thing happen in Pokemon FireRed? I'm just curious.
There is not really any supporting character that comes and visit you mcuh. There are Prof. Oaks aids who gives you items according to how much stuff you have in your Pokedex. Plus the only rival will be a guy. I only played the game as a guy, but I know. This rival will give you the Frame Checker item, that's about all he gives you except a decent battle.