Another motive could be related to a prophecy or ancient power. There could be a legend that Serena is key to unlocking some great power. An evil force might brainwash her to force her to be part of the process of obtaining that power, whether she wants to or not.
A common motive could be power. The ones doing the brainwashing might want to use Serena's power as a trainer. For example, if she has a unique bond with her Pokemon that gives them extra strength, the villains would want to control that for their own gain.
In this type of fanfiction, Serena's personality would likely change drastically. Instead of being her kind and determined self, she could become cold and calculating under the influence of the brainwashing. Her friends, like Ash and the others, would then have to find a way to break the brainwashing. They might search for a special antidote or perform a certain ritual to bring her back to normal.
The motives could be quite complex. Maybe the writer wants to show Serena's strength in a different way. By putting her in a seemingly helpless situation like being tied and gagged, it sets up a scenario where she has to use her wits and inner strength to get out of it. It could also be a form of character study, to see how Serena would react in a situation that is completely opposite to her normal, confident self in the Pokemon series. Additionally, it might be an attempt to add some edginess to the otherwise relatively family - friendly Pokemon fanfiction world.
One possibility could be that Serena gets angry when she is constantly overshadowed by other trainers in a big tournament. She might feel that all her hard work is being ignored, so she gets angry and decides to train even harder in isolation to prove herself.
Maybe Serena discovers the exciting world of Pokemon and gets completely hooked. She could start by seeing a Pokemon battle and being in awe of the power and beauty of the Pokemon. Then she might decide to start her own journey to catch different Pokemon, facing various challenges along the way.
A Litten might be a good choice for Serena. It has a fiery personality and could bring a new dynamic to her team. With proper training, it could become a powerful Fire - type Pokemon in battles against water - type opponents in Alola.
In Pokemon Ash brainwashed fanfiction, it often shows how the usually positive and determined Ash is turned into a different version of himself. This can be used to examine the relationships he has with his Pokemon and friends in a new light. For example, his Pokemon might have to find a way to break the brainwashing, which can lead to some heart - warming and action - packed scenes.
Another possible main character could be a rival trainer. Maybe someone who has been in the Pokemon world for a long time and initially looks down on Serena. But as Serena progresses, they develop a mutual respect. Also, a Pokemon professor, like Professor Oak, could be in the story. He could provide Serena with valuable knowledge about Pokemon, such as how to catch and train them.
It might be that Serena dresses Ash in a way that reflects her own dreams or desires for him. For example, she could dress him in a more elegant or refined way to make him look like a champion. This could also lead to some interesting interactions among their friends and other Pokemon trainers who notice the new look.
One possible plot could be that Serena and May meet during a Pokemon journey. They initially start as friends, sharing their experiences and knowledge about Pokemon. As time passes, they realize they have deeper feelings for each other. They might face some challenges from the Pokemon world, like dealing with a powerful villain who tries to stop their relationship because he believes it's against the norms of the Pokemon trainers' world. But in the end, they get married and continue their adventures together with their Pokemon.
Well, it could be that Ash finally realizes his deep feelings for Serena during a grand Pokemon event. Maybe they are in a beautiful, flower - filled meadow near a Pokemon Center, and Ash gets down on one knee with a Pokemon - themed ring, perhaps made from a shiny Pokemon scale or something unique.