Romance can also be a theme, although not all fanfictions go in that direction. But in those that do, it's often about the slow - burn relationship that develops between Raihan and Piers. They might start off not getting along very well, but over time, feelings start to grow.
Another theme is mutual respect. Despite their differences, they come to respect each other's skills and abilities. In many fanfictions, this respect is shown through their interactions during Pokemon training sessions or competitions.
Friendship is also a big theme. Despite their rivalry, stories often show how they respect and care for each other. For example, they might help each other in a difficult situation, like when facing a powerful wild Pokemon or dealing with a crisis in the Pokemon league. And sometimes, there are stories that develop their relationship into a romantic one, which is a less common but still interesting theme in this kind of fanfiction.
You can try fanfiction websites like Archive of Our Own (AO3). There are a large number of Pokemon fanfictions there, and you're likely to find some great ones about Raihan and Piers. Just use the search function and type in their names.
One common theme is self - discovery. Piers often has to figure out his place in the Pokemon world. Another theme is loyalty, especially towards his Pokemon. For example, in many fanfics, his Grimmsnarl is shown as a very loyal partner.
One common theme is Piers' relationship with his Pokemon. Fanfictions often explore how he trains them, the bond they share, and how it affects his battles.
Friendship is a big theme. The deep bond between Chris and Piers is a great foundation for fanfiction. Many stories show how their friendship endures through difficult times. Also, the theme of heroism comes up a lot. They are both heroic characters, and fanfiction often expands on that aspect of their relationship.
You can try searching on popular fanfiction websites like Archive of Our Own (AO3) or FanFiction.net. These platforms usually have a large collection of Pokemon fanfictions, and you might be able to find some great stories about Leon and Raihan there.
One common theme could be friendship. They might start as friends and then develop a deeper bond. Another could be mutual respect, as they recognize each other's skills and abilities.
The theme of friendship evolving into something more is also quite popular. It starts with their strong friendship as comrades in the fight against bio - threats, and then it gradually develops into a deeper, more romantic or at least more intimate relationship as the story progresses.
One interesting story could be about Piers' journey to become a better Gym Leader. In this fanfiction, he might face a new and powerful Pokemon trainer who challenges his traditional ways of leading the Gym. Another could be a story where Piers teams up with a young trainer to explore an uncharted region filled with rare Pokemon. And there might be a fanfiction that delves into Piers' past, like his childhood and how he got into Pokemon training in the first place.
Love and attraction can sometimes be a theme as well, though not always in a romantic way. It could be more about admiration and respect for each other's skills as pokemon trainers. For example, the female character might admire Ash's determination, and Ash might be impressed by her unique training methods.