There might be a 'pokedex horror story' where the Pokedex starts to give out strange and menacing messages about an upcoming disaster related to Pokémon. It warns the trainer but no one else believes it, creating a spooky situation. The trainer has to figure out if it's a real threat or just a malfunction while being constantly on edge.
The 'pokedex horror story' might be about glitches in the Pokedex system that lead to terrifying situations. For example, it could show Pokémon that are not supposed to exist or have distorted appearances. It could also be about a Pokedex that somehow predicts doom or danger related to certain Pokémon.
One of the popular characters might be the main Pokedex holder, who is often depicted as brave and curious. Another could be a rival Pokedex holder, adding some competition and drama to the story. Also, some of the Gym Leaders or Elite Four members from the original Pokemon series might make appearances and be popular in these fanfics as well.
Misty is also a character that shows up a lot. Her knowledge of water - type Pokemon can be combined with her role as a Pokedex holder. Fanfictions might explore her adventures in different regions, her encounters with new Pokemon, and how she uses the Pokedex to learn more about them.
There could be stories about the adventures of different Pokedex holders. For example, they might encounter rare Pokemon, explore uncharted regions, or face off against powerful villains. The Pokedex holders could also have unique relationships with their Pokemon that are explored in these fanfics.
One interesting story could be about a Pokedex holder's journey to discover a rare and powerful Pokemon. They might face various challenges and meet unique characters along the way.
They might have all kinds of adventures. For example, they could explore the unique Alola regions, discover new Pokémon species that are native to Alola. Charizard might also have some interesting interactions with the local Pokémon, like friendly battles or just sharing the same space. Ash could use Charizard to traverse difficult terrains in Alola, like the volcanic areas.
One idea could be a story where a trainer discovers a hidden or rare Pokemon in the Unova region that isn't fully documented in the Pokedex yet. Another could be a fanfiction that focuses on the backstories of the Unova Pokedex creators and how they came to know about all the Pokemon in the region. Maybe a story about a Pokemon that has a special ability that changes how it's classified in the Pokedex.
A Litten might be a good choice for Serena. It has a fiery personality and could bring a new dynamic to her team. With proper training, it could become a powerful Fire - type Pokemon in battles against water - type opponents in Alola.