The dude from the Seaking fishing episode? He could've been Misty's rival if the writers had thought ahead and tried to do something creative with her in mid Johto.
Or they could have brought back Marina the Golduck girl from Orange Islands, or introduced Sakura earlier. But for some reason the writers didn't want Misty/Brock to have rivals in the OS.
The OS was all heavily about Ash after all, his travel companions were lucky back then to just get a few fillers that showcased them. All the other later companions get proper showcasing, even the ones without real goals.