Maybe in the fanfiction, Jessie and May find a rare and mysterious Pokemon together. They have to work together to protect it from Team Rocket (Jessie's former group) and other villains who want to use the Pokemon's power for bad things. Along the way, they learn more about each other's dreams and pasts.
Another plot could be that there is a strange Pokemon disease spreading. Jessie and May decide to travel across different regions to find a cure. During their journey, they face many challenges like difficult terrains and other trainers who are also after the cure for their own reasons. Their friendship grows as they overcome these obstacles.
Perhaps a plot where Giovanni sends Jessie on a special mission. The mission is to infiltrate a rival organization that has some new technology that could change the Pokemon world. Jessie has to use her wits and her Pokemon's skills to blend in and steal the technology. Meanwhile, she discovers some secrets about Giovanni's past and his real motives in this power struggle.
One interesting plot could be Brendan and May going on a special quest to discover a rare and powerful Pokemon that has been lost for ages. They face various challenges and their friendship grows stronger along the way.
Often, in these fanfictions, there's a plot about the Pokemon world's reaction to Jessie's pregnancy. Some Pokemon might be curious or helpful, while others could be indifferent. There may also be a plot where Jessie has to deal with the idea of being a mother while still being a part of a villainous group. This could lead to internal conflict as she tries to balance her old life and the new responsibilities that come with having a baby.
One interesting plot could be that Ash, now in May's body, tries to enter a Pokemon Contest. He has to quickly learn the skills and grace that May has, like how to style the Pokemon in a more appealing way for the judges. Meanwhile, May in Ash's body decides to enter a Gym battle. She struggles with Ash's more straightforward and battle - focused approach compared to her Contest strategies.
Maybe Jessie's haircut is part of a disguise for a mission to rescue a captured Team Rocket Pokemon. She cuts her hair into a short bob and dyes it a different color. With this new look, she poses as a wealthy Pokemon collector's assistant. She manages to get close to the place where the Pokemon is being held, but things go wrong when one of the other assistants recognizes her as Jessie from Team Rocket. She has to use her wits and her new look to escape and still save the Pokemon.
One popular plot is Ash and Jessie accidentally swapping Pokemon. It creates a lot of humorous situations as they try to figure out how to handle each other's Pokemon. Another is when they both get stranded on a mysterious island and have to work together to survive and find a way back. They learn to respect each other's skills during this adventure.
A plot could involve a Pokemon with the ability to hypnotize others. It might hypnotize other Pokemon to make them do its bidding, and a group of trainers have to figure out how to stop it. Or perhaps a scientist is using hypnosis on Pokemon for unethical experiments, and a young trainer sets out to expose and stop this. There could also be a plot where a Pokemon trainer uses hypnosis in battles to gain an edge, but then has to face the consequences when it gets out of control.
One plot idea could be Jessie and James trying to steal a rare and powerful Pokemon that has a unique bond with a young trainer. The trainer is determined to protect their Pokemon, leading to a series of comical and action - packed encounters between them.
One idea could be Ash and Jessie teaming up temporarily to save a rare and endangered Pokemon species. They put aside their differences when they realize the importance of this Pokemon to the ecosystem.
Maybe a fanfiction where Jessie and James discover a rare and powerful Pokemon that has the ability to grant wishes. But they have to go through a series of challenges set by other mysterious Pokemon to earn the right to make a wish. This could lead to a lot of character development as they face their own greed and learn about true friendship along the way.