In a 'Naruto betrayed harem fanfiction', it could be that Naruto is blamed for something he didn't do within the harem. For example, a valuable item goes missing and the harem members quickly point fingers at Naruto. They don't believe his innocence and start to shun him. Naruto then realizes that these people he thought were his friends in the harem are not so trustworthy after all, and thus he experiences betrayal.
It could be one of the harem members who has a hidden dark side. Maybe she's jealous of Naruto's closeness to others in the harem and decides to turn the rest against him, so she becomes the main antagonist.
One popular 'Betrayed Naruto x Harem' fanfiction is 'Naruto's New Path'. In this story, Naruto is betrayed by his village in a different way than in the original series, and as he leaves, he gradually gathers a harem of strong and unique female characters who support him on his new journey. It has an interesting plot that combines action, drama, and the development of relationships within the harem.
One possible analysis could be that in such a fanfiction, the idea of Ash being betrayed might be a way to create drama. It could involve his friends or companions in the harem turning against him for various reasons like jealousy or misinformation.
One common theme is redemption. Naruto, after being betrayed, often seeks to redeem himself or prove his worth in the eyes of others, especially the females in his harem. Another theme is trust. Since he was betrayed, rebuilding trust becomes crucial in his relationships with the harem members.
Well, Mirajane could be part of the harem. She has a motherly side and would want to comfort Natsu if he was betrayed. Levy is also smart and resourceful, and she could use her skills to help Natsu out. Juvia, with her obsessive love for Gray, might transfer some of that intense loyalty to Natsu if she saw him in a desperate situation after being betrayed.
In fanfiction, Naruto being betrayed by Akeno could be a very interesting plot twist. It might start with Akeno having some hidden motives or being forced by an external power to turn against Naruto. Maybe she was blackmailed into doing so. This could lead to a whole new set of adventures for Naruto as he tries to figure out why she betrayed him and also deal with the consequences of her actions.
One common plot is that Ash's friends or some of the female characters in his harem turn against him due to a misunderstanding. Maybe they think he has some ulterior motives or has betrayed their trust in some way. Another plot could be a new character coming in and manipulating the situation to make it seem like Ash is the bad guy.
You can try fanfiction websites like FanFiction.net or Archive of Our Own (AO3). On FanFiction.net, use the search bar and type in 'Pokemon Ash Betrayed Harem' to see if there are any relevant stories. AO3 also has a large collection of fanfictions, and their tagging system can help you locate the specific type of story you're looking for.