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.
Ash would probably be initially shocked. He is used to seeing the good in people and would not expect such a betrayal from Cynthia. He might stand there in disbelief for a moment, unable to process what has just happened.
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.
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.
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.
Ash could develop his ability to understand different Pokemon cultures better. Cynthia, being from a different region, has a lot of knowledge about various Pokemon traditions. Ash could learn from her and in turn, teach her about his own experiences. This exchange could make Ash more worldly and Cynthia more in touch with the broader Pokemon community. In terms of their relationship, they could start to rely on each other more, which would be a big step for both of them character - wise.
They would become more united and responsible. Their relationship would shift from just being friends or fellow trainers to co - parents. They would need to communicate more about the baby's needs, like what kind of Pokemon - related education to give the baby.
Maybe Ash has a particular view of his own character and the way Cynthia is portrayed in fanfiction doesn't align with his idea. He might feel that the fanfiction distorts their characters or the relationship between them in some way.
Ash and Cynthia's romance began rather unexpectedly. Ash was traveling through Sinnoh when he stumbled upon Cynthia training her Pokémon. She was impressed by his determination. They then started to exchange Pokémon training tips. This led to them spending a lot of time together. As time passed, their friendship blossomed into love. They would hold hands while walking through the beautiful Sinnoh landscapes, sharing stories of their Pokémon journeys.