Well, in fanfiction, they might have an epic Pokémon battle. Ash could show off his unique battle strategies that he's developed over his journey, and Cynthia would bring her powerful Pokémon and tough battling skills. Maybe Ash's Pikachu would face off against Cynthia's Garchomp, creating a really exciting and intense showdown.
One reason is the contrast between their characters. Ash is this enthusiastic and somewhat naive trainer, always eager to learn and grow. Cynthia, on the other hand, is a very experienced and highly respected trainer. When they meet in Kanto, it creates an interesting dynamic. Fans love to see how Ash will react to someone like Cynthia and how she will view his skills.
He might meet a mysterious old trainer who imparts some unique wisdom. There could also be a young and talented trainer who becomes his rival or friend.
Ash's character in the Kanto fanfiction with Lillie might develop in terms of his leadership skills. He often takes the lead in their adventures, making decisions that affect both of them and the Pokemon they encounter. Lillie's development is more about self - discovery. In Kanto, she discovers her own strengths and weaknesses. She realizes that she has a natural ability to calm down agitated Pokemon, which she uses to help Ash during battles. Their time in Kanto is filled with challenges that shape their characters in different but complementary ways.
It could be a jealous fellow trainer. There are always those in the Pokémon world who envy the skills and achievements of others. This trainer might see Ash and Cynthia as obstacles to their own glory and decide to betray them to get ahead.
It could be about Ash achieving the ultimate goal of becoming the Kanto champion. Maybe it details his journey, the battles he had to overcome, and the growth he experiences along the way to claim the title.
Their relationship develops as they face challenges together. In Kanto, every new Pokemon they encounter, every Gym battle Ash participates in, Serena is there. She cheers him on, and through this shared experience, they grow closer. For example, when Ash loses a battle, Serena is there to comfort him, and this makes their bond stronger.
In the Kanto setting, they could explore new places together. Like when they visit the Safari Zone, they might share exciting moments while trying to catch different Pokemon. These shared experiences can lead to a deeper understanding and more affection between them. Also, meeting new trainers and learning from them could be another way. Maybe they meet an old couple who have been traveling together for years with their Pokemon, and this inspires Ash and Serena to be closer.
Ash could develop his ability to understand different Pokemon cultures better. Cynthia, being from a different region, has a lot of knowledge about various Pokemon traditions. Ash could learn from her and in turn, teach her about his own experiences. This exchange could make Ash more worldly and Cynthia more in touch with the broader Pokemon community. In terms of their relationship, they could start to rely on each other more, which would be a big step for both of them character - wise.