Team Rocket could also be the focus of a reunion fanfiction. Maybe they've reformed and are having a reunion to celebrate their new lives away from their villainous ways. They could be showing off their new Pokemon or skills that they've developed.
Obviously, Dark Ash is one of the main characters. He's the center of the story with his transformed state. Serena might also be a main character as she could be trying to reach out to Ash or deal with the new Dark Ash.
One idea could be that the main characters reunite during a big Pokemon tournament. They each have new Pokemon and strategies, and they compete against each other in an epic battle. It could also be a reunion during a crisis, like a natural disaster in the Pokemon world, and they have to work together to save Pokemon and people.
Clearly, the main characters are Ash and Misty. Ash, the protagonist of the Pokémon anime series, has his own unique style of training and a big heart for Pokémon. Misty, with her fiery personality, was an important part of Ash's early adventures. In this fanfiction, their reunion will likely be a central focus, with their different personalities and experiences coming together again. It might also involve other characters from their past who could add more depth to the story of their reunion.
He could die in a battle against a very powerful and evil Pokemon. Maybe a new, extremely strong legendary Pokemon that he underestimated, and it managed to land a fatal blow.
Barry Allen from The Flash and Rachel Berry from Glee could be main characters. Barry's speed could be used in interesting ways, like helping Rachel get to auditions on time or saving her from some danger in the city. They could form an unlikely friendship and be at the center of the story.
Gary Oak can be a great addition. He was Ash's rival and his growth and development over the series can add an interesting dynamic to the reunion. Also, Serena is quite popular to include. Her relationship with Ash and her own Pokemon journey make her a relevant character. And of course, the Gym Leaders from different regions can be brought together for the reunion, each with their own unique personalities and Pokemon.
In fanfiction, if Ash were to die in Pokemon XYZ, it would be a huge shock to the Pokemon world. His friends like Pikachu would be devastated. Maybe Team Rocket would even feel a strange sense of loss. It could lead to a whole new storyline where his friends try to avenge his death or carry on his legacy of becoming a Pokemon Master.
Obviously, the main characters would be Kendall, James, Carlos, and Logan from Big Time Rush. They are the core of any reunion story.
Obviously, Bella and Edward would be great main characters for a reunion fanfic. Their relationship was central to the original series, and a reunion could show how their love has evolved over time. They could be dealing with new challenges as a couple, like raising their daughter Renesmee in a world that still has some threats.
A young and ambitious Pokemon trainer who wants to save their injured Pokemon through surgery could be a main character. Also, the Pokemon doctor who is an expert in performing these surgeries.