Their relationship could be shown as rivals at first, constantly trying to outdo each other in Pokemon battles. Then slowly they realize their bond as twins and start to support each other.
Ash could be portrayed as more of a strategic mastermind in an Unreal Pokemon fanfiction. Instead of his usual impulsive decisions, he carefully plans out his battles, taking into account every detail of the virtual Pokemon world, like the terrain and the unique abilities that Pokemon might have in this new setting. For example, if there are floating platforms in the battle area, he'd think about which Flying - type Pokemon would be most effective to use there.
They could start with some initial jealousy or competition. For example, if the twin is also a good trainer, they might compete for the attention of a famous Pokemon trainer. But as they face challenges together, like a powerful enemy team, they realize they are stronger together and start to support each other more.
In a fanfiction plot, perhaps Ash and Richie are twins who were sent to different regions by their parents for some mysterious reason. As they grow up, they both become excellent Pokemon trainers. When they finally meet, they initially compete against each other. But then they realize that together they can achieve more. They might then explore ancient Pokemon ruins together, where they discover secrets about their family and the origin of some powerful Pokemon.
In many fanfictions, Richie is often portrayed as a very observant character. He notices things about Ash's training style and Pokemon that others might miss. For example, in some stories, he gives Ash valuable advice based on his observations.
The relationship could be one of friendship. The bimbo character could be a new friend they meet on their journey. She might be a bit ditzy but has a heart of gold. Ash and Misty could help her become a better trainer, and in return, she could bring some light - heartedness and fun to their group.
Their relationship could be portrayed as a mentor - mentee relationship in a different way. Instead of Orochimaru trying to use Naruto for his own gain, he could genuinely see Naruto's potential and guide him in the ways of some of the more esoteric jutsu. For example, Orochimaru could teach Naruto about the secrets of the snake contract without any ulterior motives. Another way is to show them as reluctant allies. Maybe there's a common enemy that is so powerful that they have no choice but to work together, and over time, they start to respect each other's abilities.
In some fanfictions, the Naruto - Sakura relationship is portrayed as a slow - burn romance. Naruto's continuous efforts to protect Sakura gradually make her fall for him. In contrast, in the original series, Sakura was mainly focused on Sasuke. Fanfiction gives an opportunity to change that narrative.
Legendaries are usually shown as very powerful and having a lot of influence. Regular pokemon are more like the normal inhabitants. For example, a legendary might be able to control the weather in a fanfic, while a regular pokemon like Pikachu is just a cute and energetic electric - type that battles in normal tournaments.
Their relationship could be portrayed as a mentor - mentee relationship. Catwoman, with her years of experience, could be teaching Batman Beyond some of the more subtle aspects of crime - fighting, like how to read a criminal's motives just by observing their body language. Another way is to show them as rivals in a different sense. Instead of just fighting over loot, they could be competing to solve a mystery first. Or, they could be portrayed as reluctant allies. They don't trust each other completely, but they know that they need to work together to stop a greater evil.
Their relationship could be portrayed as more of a brotherly bond. Goku could be like an older brother to Gohan, showing him the ropes of being a Saiyan and having fun adventures together.