For Ash, he could develop better communication skills. In the Kalos League, he often gets so focused on battles that he forgets to share his thoughts and feelings with Serena. By learning to communicate better, he can strengthen their relationship. For Serena, she could develop more self - confidence in her own Pokémon training skills. Maybe she starts out doubting herself but as the Kalos League progresses, she becomes more assertive and makes her own mark in the Pokémon training world.
You can start by looking on fanfiction.net. It has a large collection of Pokémon fanfictions, including many about Ash and Serena in Kalos. Just use the search bar and type in relevant keywords like 'Ash Serena Kalos' and you'll find a bunch of stories.
There is a fanfiction titled 'Serena's Dream in Kalos'. In this story, Serena has a big dream she wants to achieve in Kalos while Ash is there to support her every step of the way. It delves deep into Serena's character and how Ash's presence affects her journey. It's really engaging as it shows their bond strengthening over time.
They might live in a cozy cottage near a Pokémon forest. Ash could go out every day to train and catch new Pokémon while Serena takes care of their home. She could also start a small garden with Pokémon - friendly plants. At night, they'd share stories about their day over a warm meal cooked by Serena.
One possibility is that they could explore the beautiful Kalos region together. They might visit all the different gyms that Ash didn't get to fully experience before. Serena could also introduce Ash to more of the local cuisine and they could have picnics in the scenic areas of Kalos. Maybe they'd even participate in some local festivals and make new friends together.
One great fanfic could be 'A New Journey in Kalos'. It might show their adventures as they explore the new region together. They could encounter new Pokémon, and Serena might even participate in more Pokémon showcases in Kalos while Ash battles in the gyms.
A possible plot idea is that there's some sort of mystery surrounding the Kalos League. Maybe some of the Pokémon start acting strangely, and Ash and Serena have to team up to figure out what's going on. They might discover a new type of Pokémon energy or a hidden power that could change the outcome of the league. Or perhaps an old rival of Ash's from a previous region shows up in the Kalos League with a new and improved team, adding more drama to the story.
The Pokémon battles are a key element. Ash will surely face strong opponents in Kalos gyms. Another is Serena's showcases, which add a different flavor to the story. Their relationship growth also matters a lot. It could start from just being friends and gradually develop into something more.
One idea for a fanfiction could be that Ash travels to Kalos with his Infernape. There, Infernape discovers new moves or abilities inspired by the Kalos environment. It could be something related to the fairy - type energy prevalent in Kalos, which gives Infernape an edge in battles against certain opponents.
Well, in some fanfics, a common plot is Serena's growth as a Pokemon Performer with Ash being her biggest supporter. This often leads to some cute and romantic moments between them. There are also fanfics where they encounter a powerful and rare Pokemon that they have to work together to either catch or help. And sometimes, the plot revolves around Ash getting injured and Serena taking care of him, which deepens their relationship.