For the first 5 seasons, we really only think of Gary as his main rival, even though he did sort of have secondary rivalries with Richie and Casey during that time. Casey could even be considered Ash's first female rival, its just that she wasn't handled well that people don't really count her.
Richie returned in Johto during the Baby Lugia arc and got some hoso specials, as did Casey.
Yet pretty much after that the characters faded away into obscurity. Why do you think they were dropped?
Richie returned in Johto during the Baby Lugia arc and got some hoso specials, as did Casey.
Yet pretty much after that the characters faded away into obscurity. Why do you think they were dropped?