One common theme is family. Given their relationship as siblings, fanfictions often explore how they support and sometimes clash with each other due to family matters. For instance, their connection to the Aether Foundation which was founded by their family.
It could be that Lillie discovers some secrets about Gladion's past that make her understand why he left. And she might have to face some powerful enemies who are related to Gladion's past or current situation. This would be a story of Lillie's growth and her journey to reunite with Gladion.
Adventure is also a big theme. They could be on a journey through the Alola region, encountering new Pokemon and making new friends. This can show their growth as characters as they face different challenges during their adventures.
There could be a fanfiction where Lillie and Gladion are sent on a secret mission by the Aether Foundation. In this story, they discover that there are dark forces within the foundation trying to use Pokemon for evil purposes. Their bond as siblings is tested as they try to expose the truth and protect the Pokemon.
Well, it could be that Gladion has left Lillie to pursue some greater purpose in the Pokemon world, like trying to find a way to stop an impending threat. Lillie, being lost without him, might start to doubt herself at first. But as the story progresses, she could find strength within herself and decide to go after Gladion, using her own unique skills and the bond she has with her Pokemon to track him down.
One possible fanfiction could be about their early days in Alola. Maybe it shows Baby Gladion being protective of Lillie when they first encounter wild Pokemon. He could be all brave, trying to scare off the Pokemon to keep his sister safe.
In fanfiction, their relationship could be developed through moments of vulnerability. For instance, if Lillie has a nightmare about her past experiences with the Ultra Beasts, Gladion can be there to comfort her. This would deepen their bond. Also, they could train their Pokemon together. Gladion's more aggressive style and Lillie's gentle approach could complement each other, leading to a stronger relationship as they learn from one another.
One interesting plot idea could be a story where Gladion and Lillie have to team up to rescue a rare and endangered Pokemon. They might face various challenges along the way, like dealing with Team Skull. Another idea is a time - travel plot where they go back in time to learn more about their family's past and how it relates to the Pokemon world. Or perhaps a story where they are separated in a different dimension and have to find their way back to each other while making new Pokemon friends and allies.
A recurring theme is the exploration of their different personalities. Gladion's brooding and mysterious side contrasted with Moon's more open and empathetic nature. Fanfictions often play with this contrast, showing how they come to understand and accept each other. Another theme is the discovery of new powers or abilities while they are together, which not only adds to the adventure aspect but also cements their relationship as they rely on each other's newfound strengths.
Yes, there are many great 'gladion x ash fanfic' out there. You can start by looking on popular fanfiction websites like Archive of Our Own. Some might focus on their adventures together in the Pokémon world, exploring how their different personalities interact and complement each other.