There are several characters that would work well. Lillie from the Alola region could be a great addition. She has her own unique story and relationship with Pokemon that could contrast with Serena's. Another option is Kiawe. His fiery personality could create some interesting dynamics with Serena. Then there's Gladion, who could bring an element of mystery and a different approach to Pokemon battles. And of course, Professor Oak. His wisdom and knowledge of Pokemon could be a valuable asset in a Serena Pokemon fanfic. He could be the one who sends Serena on a special mission or gives her some crucial information about a rare Pokemon.
Ash could be the cause. He might accidentally break a promise to Serena, like promising to watch her perform in a Pokemon Showcase but then missing it because he got caught up in a Pokemon battle. This would surely make Serena angry.
Another possible main character could be a rival trainer. Maybe someone who has been in the Pokemon world for a long time and initially looks down on Serena. But as Serena progresses, they develop a mutual respect. Also, a Pokemon professor, like Professor Oak, could be in the story. He could provide Serena with valuable knowledge about Pokemon, such as how to catch and train them.
Definitely Ash, as he's the center of Serena's affections. But also, there could be new female characters created specifically for the fanfiction. These new characters might be trainers who are really good at Pokemon battles and catch Ash's attention. Serena would then become jealous of their skills and the attention Ash gives them. Additionally, any of Ash's Pokemon that seem to have a special connection with another character could also be part of the scenario that makes Serena jealous. For example, if Pikachu seems to like a new girl more than Serena, that could be a reason for her jealousy.
Ash is a great character to pair Serena with. Their history from previous adventures adds depth to the story. They could have new adventures together in Alola, with Ash showing Serena the ropes of the Alolan Pokemon world and Serena sharing her own unique skills. Another good option is Lillie. Serena and Lillie could bond over their love for Pokemon. They could help each other grow, like Serena teaching Lillie more about Pokemon battles and Lillie introducing Serena to the unique Alolan Pokemon.
A group of poachers could be the kidnappers. They might think that Serena has information about the location of rare Pokemon in the areas she has traveled. They want to use her to find these Pokemon so they can capture and sell them on the black market.
Often, Team Rocket can be the main antagonists. They might be after a rare Pokemon that Clement and Serena have or are protecting. Their sneaky ways and desire for power can create a lot of trouble for our heroes.
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.
Serena would do well with a Delphox, the evolved form of Fennekin. It has strong fire - based attacks. Additionally, an Altaria would be a wonderful addition. It's a flying - type with a graceful appearance. For Calem, Greninja would be a superb choice. It's extremely agile and has great water - type attacks. And a Tyranitar could be in his team too, as it's a very tough and powerful Pokemon.
Well, obviously Ash and Serena are the main characters. Ash is the determined pokemon trainer always on a quest to be the best. Serena is the girl with a big crush on Ash. She is also a skilled trainer in her own right and has her own dreams related to pokemon, like performing in pokemon shows.