Perhaps in this high school fanfiction, Serena is a new student. Ash, being popular for his Pokémon knowledge, is tasked to show her around. They start to develop feelings as they explore the school's hidden Pokémon habitats together. They then have to defend these habitats from a group of bullies who want to destroy them.
A possible plot could be that Ash and Serena are part of a high school project to study different Pokémon regions. They are paired together and during their research, they discover a rare Pokémon. But to catch it, they need to overcome their own insecurities and also deal with a jealous classmate who tries to sabotage their efforts.
One idea could be that Ash and Serena are in a high school where there's a Pokémon battle club. Serena is trying to improve her battling skills to be more like Ash. They face a rival couple in a big tournament which tests their relationship as well as their Pokémon skills.
One idea could be that Ash and Serena are paired up for a big school project. They start off not getting along well because of their different approaches, but as they work together, they discover new things about each other and their friendship deepens. Maybe they have to research a rare Pokemon that has a connection to their town's history.
One plot idea could be that Ash and Serena are paired up for a school project about Pokémon evolution. During their research, they discover a rare Pokémon in the schoolyard that has an unusual evolution method. This discovery brings them closer as they work together to document it and share their findings with the school.
A possible plot is that Ash is completely oblivious to Serena's yandere nature at first. Serena starts leaving little gifts for Ash that are laced with a hidden meaning only she understands, like a charm that she believes will keep him close to her. As the story progresses, Ash begins to notice Serena's strange behavior when she gets extremely jealous over small things, like when he just has a friendly chat with a female Pokemon. This leads to a conflict within their relationship as Ash tries to figure out what's going on with Serena.
One idea could be that they embark on a new adventure in a region neither has visited before. They face unique Pokémon and challenges together, which strengthens their bond. For example, they might come across a rare Pokémon that is said to only appear to those with a strong connection. As they work to catch it, they realize their feelings for each other have deepened.
Perhaps the child gets lost in a mysterious forest while trying to follow in their parents' footsteps as a Pokémon trainer. Along the way, they meet various Pokémon that help them find their way back, teaching the child about friendship and the bond between humans and Pokémon. The child could also learn some new skills from these Pokémon encounters.
One idea could be Ash and Serena having a child who shows an extraordinary talent for Pokémon battles at a very young age. The story could focus on how they train and guide their child, just like how Ash was trained by his mentors. Another plot could be them facing a new and powerful villain who threatens their family, and they have to work together with their Pokémon to protect their home and each other.
One idea could be Ash joining the high school's Pokemon battle club and facing off against rivals who have different battling styles. He might learn new strategies and form new friendships along the way.
In high school, their relationship could start with small things like sharing Pokémon treats during lunch break. As time passes, they might study together for Pokémon biology classes. Ash could help Serena train her Pokémon in the schoolyard, which would bring them closer.
Maybe there's a plot where they participate in a high school competition. It could be a sports competition or an academic one. Ash's determination and Serena's grace under pressure could shine through. They might have to compete against other students who are also their rivals in some way, adding more drama to the story.
Well, perhaps in the fanfiction, Serena could design her own wedding dress inspired by her Pokemon performances. Ash, on the other hand, might get some advice from his old friends like Brock on how to be the perfect groom. And they could have a wedding ceremony where all their Pokemon use their special moves to create a beautiful display in the sky.