It's also possible that an evil organization is behind Ashley's betrayal. The organization could be the main antagonist as they are using Ashley as a tool to get to Ash and his Pokemon. They might have their own sinister plans for the Pokemon world, and Ash's Pokemon are somehow a key part of it.
Maybe there is an evil Pokemon trainer who has influenced Ashley to betray Ash. In this case, that trainer would be the main antagonist. He or she might have promised Ashley something in return for her betrayal, like rare Pokemon or power.
It could be a jealous rival trainer. This trainer might have always been envious of Ash's popularity and the loyalty of his harem. So, they plot and scheme to turn the harem against Ash by spreading lies and creating discord among them.
It could be a new and powerful trainer who has a vendetta against Ash. This trainer might see Ash as a threat to their own rise to the top in the Pokemon world. They could manipulate Leaf into betraying Ash to further their own goals.
It could be a powerful and jealous Galar trainer. This trainer might see Ash as a threat to their own reputation and success in the region. They would then use their influence and charm to turn Ash's friends against him.
It could be a group of Team Rocket - like villains. They are after the unique powers that the reborn pokemon might possess. Since the reborn pokemon has a human - like intelligence, they see it as a valuable asset to use for their evil plans, like stealing all the precious pokemon resources or taking over a certain region.
It might be a rogue ninja from the Wave. They could have a vendetta against Konoha and see Naruto as an easy target to frame and cause chaos between the two places.
A new, original villain could also be the main antagonist. This villain could be someone from Percy's past who has a grudge against him and wants to use the Avengers as a way to get revenge. By making Percy betray the Avengers, this villain can not only harm Percy but also cause chaos among the powerful superhero group.
Obviously, Kami would be the main antagonist. Since the title says 'naruto betrayed by kami', Kami is the one doing the betraying, which makes him the bad guy in this fanfiction.
It could be a new and powerful trainer who manipulates Anabel into betraying Ash. This trainer might be jealous of Ash's success and see Anabel as a means to bring Ash down.
In some cases, it could be an ancient and evil magical being that has been awakened. This being has the ability to manipulate people's minds and convinces everyone that Harry is evil. It wants to isolate Harry before attacking him directly for some unknown but dark reason.
A powerful and envious Pokémon trainer could be the main antagonist. This trainer might be jealous of Ash's bond with Greninja and decides to break it. He could use dark magic or some sort of mind - controlling device to make Greninja turn against Ash.