In this kind of 'ash and riolu betrayed fanfic', it might be that Ash and Riolu are in a Pokémon tournament. They meet a new trainer who seems friendly and offers to team up with them. However, during the tournament, this so - called friend betrays them by using underhanded tactics. This could include things like secretly weakening Riolu before a battle or spreading false rumors about Ash to other trainers. As a result, Ash and Riolu not only lose the tournament but also feel deeply hurt and betrayed.
One idea could be that Ash is betrayed by his so - called friends in the Pokémon world. They might be jealous of his status as the Chosen One and team up against him. For example, Gary could spread false rumors about Ash, causing other trainers to doubt him.
In a fanfic where Ash betrays and captures Arceus, it could be a very dark and unexpected turn. Maybe Ash has been influenced by some powerful and malevolent force. This would completely change his character archetype from the heroic trainer we know. It could lead to a lot of chaos in the Pokémon world as Arceus is like a god in that universe.
It could be that Ash discovers some sort of secret about Harrison that he misinterprets. Instead of talking to Harrison about it, he takes actions that seem like a betrayal. For instance, Ash might tell others about this secret, thinking it's for the greater good, but it actually causes a lot of harm to Harrison.
In such a fanfic, perhaps Ash and Paul were on a journey together in the Pokémon world. They might be part of a team for a big tournament. Then, one of them could make a deal with a rival group behind the other's back for personal gain, like getting access to a rare Pokémon. This would be the betrayal.
It's mainly Ash and Paul. But depending on the plot of the fanfic, there could be other trainers or characters involved. For instance, a new trainer who comes in between them and somehow instigates the betrayal. Or a Pokémon professor who might unknowingly play a part in the events leading to the betrayal.
Obviously, Ash and Riolu are the main characters. Ash is a well - known Pokémon trainer, and Riolu is a Pokémon. There might also be other characters who play a role in the betrayal, like the one who betrays them, which could be another trainer or a Pokémon.
Another common theme is redemption. After being betrayed, Ash usually has to find a way to rise above the situation. He might have to re - evaluate his relationships and his own journey as a champion.
One popular 'ash betrayed fanfic' could be about Ash being betrayed by his so - called friends in the Pokemon world. Maybe they wrongly accuse him of something he didn't do, like stealing a rare Pokemon. This could lead to Ash having to prove his innocence while also dealing with the emotional pain of the betrayal.
Perhaps in the fanfic, a new and mysterious Pokémon arrives. This Pokémon is able to manipulate the thoughts of those around it. It makes Mewtwo believe that Ash is a threat to all Pokémon. So Mewtwo starts to act against Ash. Ash, on the other hand, is clueless as to why Mewtwo has suddenly turned on him. He has to dig deep into the secrets of this new Pokémon and find a way to reverse what it has done to Mewtwo.