It could be that Lillie betrays Ash because she believes it's the only way to achieve a greater good in the Pokémon world. She might think that Ash's methods are too dangerous or not in line with what she believes is right for the future of Pokémon and humans alike. This would create a complex conflict between their ideologies.
Ash would be extremely hurt. He's a very loyal person, and having someone he cares about like Lillie betray him would be a huge blow. He might initially go into denial, not believing that Lillie could do such a thing.
The plot could involve a threat to Alola. Ash and Lillie, now in love and getting married, have to put their wedding plans on hold to save the region. Along the way, they discover that their love gives them extra strength. They defeat the threat together and then have a grand wedding celebration, which is attended by Pokemon trainers from all over the world.
The plot could revolve around a new, powerful and mysterious Pokemon that appears. Ash and Lillie both set out to catch it. Their paths cross, and they end up in a friendly competition to see who can befriend the Pokemon first. Along the way, they have Pokemon battles to show their skills and determination. This could lead to a deeper understanding between them and a new chapter in their respective Pokemon journeys.
One interesting idea for the fanfiction is that May betrays Ash to protect her family. An evil group threatens her family and the only way to save them is to turn against Ash. This would create a complex situation where May is torn between her loyalty to Ash and her love for her family. Ash, on the other hand, would be completely blindsided by her sudden change in behavior.
In 'pokemon ash x dawn betrayed fanfiction', it could be that Dawn betrays Ash for personal gain. For example, she might be tempted by a powerful trainer or organization that offers her something she desires, like a rare Pokemon or a chance to become a more famous trainer. This betrayal could lead to Ash feeling heartbroken and confused, and it might set off a series of events where he has to deal with his emotions as well as the consequences in his Pokemon journey. It could also involve their friends and other Pokemon getting involved in the aftermath of this betrayal.
One possible plot could be that within the fanfiction world, there is a new character introduced who seems to be a great ally at first. This character gains the trust of Ash and Brock over time. However, this new character has a hidden agenda. They might be from a rival region and their goal is to undermine Ash and Brock's reputation in the Pokemon world. So they start spreading false rumors about them and turn other trainers against them, thus betraying their new - found friendship.
Well, perhaps Clemont betrays Ash because he becomes envious of Ash's success. Maybe he gets influenced by some dark force in the Pokemon world that convinces him to steal Ash's Pokemon or to lead him into a dangerous trap.
It could also be about them exploring a new aspect of the Pokemon world, like a hidden dimension. In this dimension, they have to rely on each other completely. Ash's combat skills and Lillie's ability to communicate with certain Pokemon types might be crucial in their survival and discovery. As they progress, their bond deepens and they learn more about themselves and the Pokemon world around them.
I'm not sure specifically as there could be many different takes in fanfiction. It might involve scenarios where Ash and Lillie break someone's trust, perhaps in the context of their adventures or relationships within the fan - created story.
One common theme is adventure. Since they are both Pokemon trainers in the Pokemon world, they often go on adventures together in the fanfictions, exploring new regions and encountering new Pokemon.