Well, a 'pokemon double trouble fanfic' could be about all sorts of things. It might be a story where two Pokemon get into some kind of mischief or face a double - sized trouble together. Maybe it's about two trainers who have Pokemon that cause double the chaos during a battle or an adventure.
One idea could be to have two rival trainers who both accidentally release two extremely rare and powerful Pokemon at the same time, causing double the chaos. These Pokemon could be a legendary pair that are known to cause trouble when together, like Ho - Oh and Lugia. Their combined powers could disrupt the balance of the Pokemon world, and the trainers must work together despite their rivalry to calm them down.
The main characters could be a pair of best friends. One friend could be a very cautious and methodical trainer, while the other is more impulsive. They both encounter a double - trouble situation when they come across two wild Pokemon that have been affected by a strange energy. These Pokemon start attacking everything in sight, and the two friends have to combine their different training styles to subdue them. For example, the cautious friend might try to analyze the Pokemon's behavior first, while the impulsive one jumps right into battle.
Harry Potter is bound to be one of the main characters. Since it's about 'double trouble', there could be a version of Harry that is different in some way, like an evil Harry or a Harry from an alternate dimension. Ron and Hermione would be there to support the real Harry. Dumbledore might also play a significant role as he often has the wisdom to deal with complex situations. And, of course, Voldemort could be a central figure as well, as he is the main antagonist in the Harry Potter series and any double trouble might be related to the battle against him.
One common theme could be friendship. Since it's 'double trouble', it might involve two characters getting into various situations together and their bond growing through it.
One possible plot idea could be two versions of Harry Potter existing simultaneously in Hogwarts, causing chaos as they both try to deal with Voldemort in different ways. Another could be that a spell creates double trouble for Harry, like his magic splitting into two opposing forces that he has to reconcile.
One common theme is identity. Since it's about double life, characters (either trainers or pokemon) often struggle with who they really are. Another theme is secrecy. There's always something hidden about their second life. For example, a pokemon might be a powerful guardian in its other life but just a normal pokemon in the eyes of its trainer.
It could be about a trainer facing two difficult choices regarding their Pokemon. For example, having to choose between evolving two different Pokemon that both have great potential but in different ways.