Well, one possibility could be that Mavis has some sort of hidden agenda. Maybe she's being controlled by a greater evil force that makes her turn on Naruto. It could also be a misunderstanding. For example, false information is spread about Naruto, and Mavis believes it without proper investigation. Another idea is that Mavis has a different view of the ninja world compared to Naruto, and their conflicting ideologies lead to her betraying him.
In a fanfiction scenario where Naruto is betrayed by Mavis, it might start with a build - up of trust between them. They could be working together on a mission or towards a common goal in the ninja world. But then, Mavis discovers something about Naruto's power or origin that scares her. For instance, if Naruto has some connection to a dark entity that he's unaware of, and Mavis, in her fear, decides to betray him to protect the world as she sees it.
One possible plot could be that Naruto, with his strong ninja skills, and Mavis, with her magical knowledge, team up to protect their world from a new, powerful threat. Their marriage brings together the ninja and magical worlds in a unique alliance.
One possible plot could be that Naruto, being a curious ninja, somehow ends up in the world of Hotel Transylvania. He meets Mavis and they become friends. Naruto could show Mavis some of his ninja skills, like creating clones or running on water. They might team up to solve a problem in the hotel, like when a group of mischievous vampires cause trouble. Naruto's positive attitude and determination could inspire Mavis to be more adventurous outside of the hotel's usual routine.
He could feel a great sense of anger and sadness. Naruto has a big heart, and being betrayed by someone he considered a friend or ally would be deeply hurtful. He might start to question his own judgment in trusting Mavis. And then, he would likely try to find out the reason behind the betrayal. He's not the type to just let it go. He would pursue the truth, whether it's to get revenge or to clear up any misunderstandings.
In this fanfiction, it might be that Sirzechs is being manipulated by some dark force. This dark force convinces Sirzechs that Naruto is evil. As a result, Sirzechs betrays Naruto. Naruto then has to not only deal with the betrayal but also figure out how to stop this dark force that is causing so much chaos and misunderstanding.
Perhaps in this fanfiction, Yugao is secretly working for a hidden organization that wants to get rid of Naruto. She betrays him by revealing his secrets or setting him up in dangerous situations. Naruto, being the kind - hearted person he is, initially doesn't want to believe she would do such a thing and tries to reason with her, but she is too far gone in her loyalty to the other side.
In this fanfiction, perhaps there's a power struggle. Naruto, being a powerful ninja, could be seen as a threat to the RWBY world's power balance. So, the RWBY characters, out of fear or a sense of self - preservation, betray him. They might think he'll disrupt their way of life or take over their territory.
One possible plot could be that Jiraiya is forced to betray Naruto due to some external threat. Maybe an enemy has captured Jiraiya's loved ones and threatened to kill them if he doesn't turn on Naruto. Jiraiya, in a difficult position, might have to pretend to be against Naruto to protect his loved ones while secretly trying to find a way to free both Naruto and his family from the enemy's clutches.
Well, it could be that Kurenai is somehow deceived into believing Naruto has done something really bad. Maybe she's tricked by an enemy who fakes evidence against Naruto. So, in her misunderstanding, she turns against him.
In this fanfiction scenario, perhaps Mirajane has her own dark secrets or hidden motives that lead to her betraying Naruto. She might be seeking power and sees Naruto as an obstacle. Or, it could be related to loyalty to her own guild or group. If there are conflicting interests between Naruto's world and her world, she might choose to side against Naruto to protect her own people.
Well, it could be that they betray their village. Maybe they are tricked into believing false information about Konoha being corrupt. So they side with an enemy force, thinking they are doing the right thing.