Betrayal could also stem from a misunderstanding. Maybe Ash or Cynthia accidentally offend someone without realizing it. For example, they might unknowingly step on a trainer's dreams or beliefs. And that trainer, feeling deeply hurt, decides to betray them. Or it could be that a Pokemon they both have a connection with has a different loyalty that they were not aware of, which leads to the Pokemon causing their betrayal.
One possible plotline could be that Ash and Cynthia are betrayed by a powerful and long - hidden organization in the Pokemon world. Maybe they are lured into a trap under false pretenses. For example, they are told there is a great Pokemon discovery but it's actually a setup to steal their Pokemon or get some important information from them. Another could be a betrayal from a so - called friend. This friend might be jealous of their achievements and decides to side with an enemy to bring them down. This could lead to Ash and Cynthia losing battles they should have won and facing challenges that seem insurmountable at first.
One possible plotline could be that Ash and Cynthia are betrayed by a powerful villain who they once trusted. This villain might have been secretly working against them all along, perhaps stealing their Pokémon or sabotaging their quests. For example, the villain could be a rival trainer who was jealous of their success.
It could also be due to competition. Sabrina might see Ash as a threat to her status as a powerful trainer. If Ash starts to gain more recognition and success, Sabrina, being prideful, could feel betrayed as if Ash is trying to overshadow her and thus take actions against him.
It could be a jealous fellow trainer. There are always those in the Pokémon world who envy the skills and achievements of others. This trainer might see Ash and Cynthia as obstacles to their own glory and decide to betray them to get ahead.
One possible reason could be jealousy. Maybe his friends are jealous of Ash's success in his Pokemon journey. For example, if Ash wins a big tournament and gets all the fame, his friends might feel left out and betrayed. Another reason could be a misunderstanding. Ash might do something that his friends misinterpret. Say he makes a deal with an enemy in order to save his Pokemon, but his friends don't understand the situation and think he's turned on them.
Perhaps in this new region, Ash discovers a powerful new Pokemon that others want to control. His friends, fearing the power of this Pokemon, betray him to protect the region. They might think that Ash is being too reckless with this new discovery and that it could lead to destruction. It could also be that there's a prophecy in the new region that Ash is somehow involved in, and his friends misinterpret it and believe he's the cause of potential harm.
One reason could be power. Maybe he was offered a great deal of power by an outside force in exchange for betraying the harem. Another could be jealousy. If there was someone in the harem who was getting more attention or was more successful than him in some way, he might have been driven by envy to betray them.
One possible plotline could be that Ash's new friends in Galar turn on him due to some misunderstanding. Maybe they think he's trying to steal the spotlight in Pokemon battles. For example, if Ash wins a big tournament that some local trainers had high hopes for. Another could be that a villain in Galar manages to manipulate those around Ash into believing he's a threat to the Galar region. This could be by spreading false rumors about his intentions with powerful Pokemon. Or perhaps there's a new type of Pokemon in Galar that has some sort of mind - controlling ability and it's used on Ash's friends to make them betray him.
One possible plot could be that Cynthia, perhaps in a quest for power or influenced by some dark force, betrays Ash. Maybe she steals his Pokémon to use in her own battles or to offer to a powerful villain in exchange for something she desires, like rare Pokémon or access to a powerful training ground.
One possible scenario could be that Ash betrays May for a powerful Pokemon. Maybe he gets offered a super rare and strong Pokemon but has to cut ties with May to get it. Another could be that May betrays Ash because she is influenced by a rival trainer who convinces her that Ash is holding her back from reaching her true potential as a Pokemon trainer.