Well, perhaps a plotline where Ash discovers that being the chosen one means he has a connection to an ancient Pokémon prophecy. This prophecy might involve saving the Pokémon world from a looming disaster. Along the way, he might gain new Pokémon partners that are specifically destined to help him in this grand task. He could also face challenges from other trainers who are jealous of his chosen - one status.
In some 'ash ketchum the chosen one fanfiction', there could be a plotline where Ash's role as the chosen one is tied to a hidden realm in the Pokémon world. He has to enter this realm, which is filled with powerful and mysterious Pokémon. There, he must learn ancient techniques and gain new knowledge. As he does this, he also has to deal with a group of villains who want to use the power of the hidden realm for their own evil purposes.
In this fanfiction, Gary could be an important character. Since he has always been in competition with Ash, he might have mixed feelings about Ash being the chosen one. Serena could also be a main character. She might be inspired by Ash's chosen - one journey and decide to follow him, offering her own skills and support. Professor Oak would likely be involved as well, guiding Ash with his vast knowledge of Pokémon.
A possible plotline is that Ash gets a mysterious illness that affects his ability to communicate with his Pokémon. This causes chaos among his team as they don't understand why he's acting differently. Meanwhile, Team Rocket might try to take advantage of Ash's weakened state but end up having a change of heart when they see how sick he really is.
Well, in some Ash Ketchum high school fanfictions, there's a plotline where Ash is given the task of training a group of beginner Pokémon trainers in the school. He has to use his own experiences to teach them, which is not easy as they all have different personalities. Also, there could be a plot where Ash is framed for something he didn't do in the Pokémon - related incidents at school, and he has to prove his innocence while still focusing on his Pokémon training and studies.
One interesting aspect is his growth. In fanfiction, we can see how he becomes a more skilled trainer over time. For example, he might learn new battle strategies.
One possible plotline could be that a villain uses a new type of Poké - ball technology to control Ash's mind and make him do their bidding, like stealing Pokémon from other trainers. Another could be a strange psychic Pokémon that accidentally takes over Ash's mind while trying to communicate, leading to some chaotic and comical situations as his friends try to figure out what's wrong and break the control.
One plotline could be Fem Harry trying to keep her magical abilities a secret in the Pokemon world while also trying to fit in as Ash's daughter. Another could be her using her magic to help Ash in a particularly difficult Pokemon battle. Maybe she uses a spell to make a Pokemon stronger or to break an opponent's tricky move.
One possible plotline could be that Ash, as a girl, has to face different challenges in the Pokémon world. For example, some trainers might underestimate her at first. She could also form new friendships or rivalries. Maybe she'd have a different approach to training Pokémon, focusing more on strategy and less on brute strength like she sometimes did as a boy. Another aspect could be how her Pokémon react to her new form. Some might be more protective, while others could be confused at first but then adapt.
One common plotline is that Ash has to find and assemble a group of special Pokemon that are key to saving the world. Another is that he has to master a new and powerful type of Pokemon training exclusive to the Chosen One.
One interesting story could be about Ash Ketchum competing in a super - secret and high - stakes Pokémon tournament where he has to use his skills in new and unexpected ways. Another might be a story where he teams up with some rare and powerful Pokémon that he discovers in a hidden region. And there could also be a fanfiction where Ash has to face his own doppelganger who is causing chaos in the Pokémon world.
One interesting story could be where Ash and Alexa go on a journey together in a region neither has explored before. They encounter new Pokémon and face challenges side by side. Maybe they have to work together to solve a mystery involving a rare Pokémon that has been causing trouble in the area.