Ash Ketchum is an obvious choice. He's the main character in the original series and has a lot of room for different storylines in fanfiction. You can explore his journey in the Indigo League from different perspectives, like what if he had made different choices during battles.
Another plot idea is to have a story centered around a Pokemon that has been misjudged in the Indigo League. Maybe it's a dark - type Pokemon that everyone assumes is evil. But the main character, a trainer, sees its potential and trains it to become a champion - level Pokemon. The trainer has to overcome the stigma associated with the Pokemon type and prove that it can be just as strong and noble as any other Pokemon.
One interesting Pokemon Crystal fanfiction could be about a trainer who discovers a hidden ability in their Cyndaquil that no one has ever seen before. This new ability changes the way they battle and makes them a target for both jealous trainers and curious researchers.
Ethan or Lyra are often popular. They are the main characters in the games, so in fanfiction, they are usually the center of many adventures. Writers like to expand on their journeys, give them new challenges, and develop their personalities further.
There are often fanfictions that focus on the relationships between trainers and their Pokemon. For example, a story might tell about a trainer in Pokemon Silver or Crystal who has a special bond with their Pikachu. They go through different challenges together, like facing a powerful Gym Leader. The Pikachu might evolve in a unique way because of their strong bond, which is different from the normal evolution process in the games.
Another option is to check out some Pokemon - focused forums. There are often sections where fans share their own fanfiction. You might need to do a bit more digging around, but you can find some unique and interesting Pokemon Crystal rival fanfiction there.
One great Pokemon Crystal rival fanfiction could be about the rival's hidden backstory. Maybe he has a family in a far - off region that he's trying to make proud, which is why he's so competitive in the Johto region.
Ash is definitely one of the most popular. He's the main character from the original Pokemon series and has a huge fan base. People love writing about his adventures with Crystal. Crystal herself is also very popular as she brings a new dynamic to the story. Pikachu, Ash's trusty partner Pokemon, is also often a central figure in these fanfictions.