Ash is often a popular choice. Since he has such a strong bond with Pokémon, it's easy to imagine scenarios where he is possessed by a Pokémon spirit. Another one could be Misty. Her feisty personality could lead to interesting storylines when combined with Pokémon spirit possession.
Well, Gary Oak is a character that shows up in a lot of 'pokemon spirit possession fanfiction'. He's a rival, and having him be possessed by a Pokémon spirit can add a whole new layer to his rivalry with Ash. Also, Jessie and James from Team Rocket are quite popular. Their villainous nature can be twisted in interesting ways when they are possessed by Pokémon spirits, perhaps leading to them having a change of heart or becoming even more devious.
In many 'pokemon spirit possession fanfiction', Brock is also involved. His knowledge of Pokémon and his nurturing side could be enhanced or changed by a Pokémon spirit possession. Additionally, characters like May and Dawn have also been used in such fanfictions. May's determination and Dawn's elegance can be combined with the unique traits of a possessed Pokémon spirit to create engaging storylines.
In Pokemon birth fanfiction, Misty can be a popular character. She has a strong connection with water - type Pokemon, and she could be involved in the birth of a water - type Pokemon, perhaps using her knowledge of water to create a suitable environment. Professor Oak is also a character that often shows up. His vast knowledge of Pokemon would make him a valuable asset during a Pokemon birth. And Pikachu, as Ash's most famous Pokemon, might also be part of the story, either as a helper or just being curious about the new - born Pokemon.
Ash Ketchum is often involved. He's a well - known trainer, and in fanfictions about pokemon egg laying, he might be in a situation where he discovers a rare Pokemon egg and has to figure out how to take care of it. Another popular character is Misty. She could be involved in stories where she uses her knowledge of water - type Pokemon to help with the hatching process of a water - related Pokemon egg.
Ash and Serena are often the main characters. Their relationship in the Pokemon anime has a lot of potential for amorshipping fanfiction. Ash's determination and Serena's grace make for an interesting dynamic in the stories.
Often, young and ambitious trainers are involved. They might be curious about Pokemon abilities and conduct their own little experiments. Scientists also play a big role. They usually have the resources and knowledge to carry out more complex experiments on Pokemon in a more formal setting.
Naruto himself is often involved. Since he has a strong will, it's interesting to see how he would deal with being possessed or using the possession jutsu. Sasuke is another common character. His dark past and powerful abilities make for great storylines when combined with possession jutsu.
In some 'pokemon champion ash fanfiction', Gary could be an important character. He has always had a competitive relationship with Ash, so in stories where Ash is a champion, Gary might try to challenge him or be involved in some sort of plot related to Ash's championship. Another character could be Serena, especially if the fanfiction focuses on the romantic aspect of Ash's life along with his championship journey.
In many fanfictions, Gary Oak can also be a significant character. Since Ash is smart in these stories, there could be a rivalry between him and Gary where they constantly outwit each other in Pokemon battles and in their knowledge of Pokemon lore. Another character could be Professor Oak, who might be amazed at Ash's new intelligence and give him special tasks or Pokemon to train.
Definitely Dawn. And then there are her traveling companions. May, if she were to make an appearance in a crossover type of fanfiction, could be involved. May might be curious about Dawn's experiences with tickling in the Sinnoh region. Also, Nurse Joy could potentially be part of the story. Maybe Dawn gets tickled by a Pokemon while at the Pokemon Center and Nurse Joy has to deal with the resulting chaos and laughter.
Naruto himself is obviously very popular in these fanfictions as the main character. His decisions are the central focus. Sasuke is also commonly involved. Since Sasuke's actions and decisions often intertwine with Naruto's, fanfiction writers like to explore how different decisions from Naruto would affect Sasuke's path. For example, if Naruto made a decision that could sway Sasuke from his revenge - seeking journey.
Naruto is often involved. Since he has the ability to transform into the Nine - Tails in the original series, fanfiction might expand on this by giving him more shapeshifting abilities or different forms of the Nine - Tails transformation. For example, a more powerful and controlled version of the full - Nine - Tails form.