His rival, Gary, could be a likely candidate. Gary has always been competitive with Ash, and in this fanfiction, his jealousy could reach a boiling point, causing him to betray Ash for his own gain, like trying to steal his Pokémon or get credit for his achievements.
Well, without actually reading the specific fanfiction, it could be about Ash Ketchum, who is in a 'godlike' state, being betrayed by someone. Maybe his friends turn against him due to jealousy of his newfound power. Or perhaps an enemy manages to deceive those close to him, making them think Ash has done something wrong when he hasn't.
One common theme could be Ash being betrayed by his friends in the Pokémon world. For example, they might leave him for a more powerful trainer or because of a misunderstanding. Another theme could be betrayal by the Pokémon League, like being wrongly disqualified from a major tournament. Also, some fanfictions may explore Ash being betrayed by a new character who has ulterior motives and tries to undermine his journey.
Perhaps in this fanfiction, Ash is betrayed by a mentor figure. This person has been guiding him all along but has a hidden agenda. The rated m aspect could mean there are some intense battle scenes and moral dilemmas. Ash will have to reevaluate his beliefs and skills to overcome this betrayal and the challenges that come with it.
At first, Ash would be in shock. But then, he would likely turn his focus on finding out the truth. He's not one to give up easily. He'd start investigating what led to his betrayal. He might even go on a journey within the RWBY world to find evidence to clear his name and expose those who really are at fault. He'd still hold out hope that his former friends would see the truth and come back to his side.
Gary Oak could be a likely betrayer. He has always been Ash's rival, and in some fanfiction, he might take things too far and betray Ash in a crucial Pokémon battle, like using underhanded tactics to win. This would surely make Ash cry.
One possible plot could be that Ash, being from a different world, is initially welcomed into the RWBY universe. But then, he might be betrayed when his Pokémon powers are seen as a threat. Maybe the RWBY characters fear that his abilities could disrupt the balance of their world. For example, if his Pikachu's electricity causes unexpected power surges in a world that has its own unique energy sources like Dust.
A possible theme is the betrayal by a mentor figure. Suppose an older, more experienced trainer that Ash looked up to gives bad advice on purpose, leading to his defeat. This would make Ash feel both betrayed and sad, crying over the loss of trust and the failure in his Pokémon journey.
Maybe a new, mysterious villain who has a grudge against Ash or wants to use his skills for their own evil purposes. This villain might be from a far - off region and has special powers that allow them to hypnotize people. They see Ash as a useful tool to carry out their plans in the Pokémon world.
Ash could become more confident and wise as a Dragon Master. His decision - making skills would improve as he deals with powerful and often unpredictable dragon Pokémon.