One possible reason could be a misunderstanding. Maybe Anko thought Naruto was involved in something dangerous or against the village rules without having all the facts. For example, if there was some sort of strange activity in the village and Naruto was in the wrong place at the wrong time, Anko might jump to conclusions and attack him.
One possible reason could be a misunderstanding. Maybe Hermione thought Snape was involved in some dark plot against her friends. In the wizarding world, there are often secrets and deceptions, and if she got some false information, it could lead her to take such drastic action.
One possible reason could be a misunderstanding. Maybe Anko was involved in a mission that Naruto thought was unjust, and he misjudged her actions as being malicious. For example, if she had to capture someone Naruto considered a friend, even if it was for the right reasons from Anko's perspective, Naruto might hold a grudge.
One possible reason could be a miscommunication between them. Maybe Anko feels neglected and then strays. Another reason might be that the writer wants to create a more complex and angsty plot.
Maybe she loves the Naruto world so much. The unique characters, like Naruto himself with his never - give - up attitude, and all the different jutsus and storylines in the original Naruto series make her want to explore more in fanfiction.
One possible reason could be unrequited love. Maybe Naruto has deep feelings for Anko, but she doesn't feel the same way. She might be focused on other things like her ninja duties or she could have feelings for someone else. Another reason could be that Anko betrays Naruto's trust in some way. For example, she might break a promise she made to him that was really important. It could also be that Anko does something that goes against Naruto's ideals, which makes him feel heartbroken as he had a different image of her in his mind.
Perhaps Anko has a personal connection to Naruto. Maybe she sees a bit of herself in him, like his determination in the face of difficulties, and this makes her feel a sense of kinship and thus the need to protect him.
One possible reason could be extreme jealousy. Sakura might be so blindly in love with Sasuke that she sees Naruto as a threat to Sasuke's attention or her relationship with Sasuke. Maybe she thinks Naruto is getting in the way of Sasuke's return to the village or her attempts to win Sasuke back.
I'm not sure if there is an exact fanfiction with this title. But if it exists, a possible plotline could be that Anko discovers Naruto's so - called 'cheating' through some misunderstanding. Maybe she sees Naruto with another girl in a compromising situation that is actually innocent. This could lead to a rift in their relationship, and Naruto would then have to work hard to clear his name and win Anko back.
One possible storyline could be that Anko tries to subtly show her feelings to Naruto. For example, she might start offering to train with him more often. She could also be protective of Naruto in dangerous situations, which Naruto might initially mistake for her just being a good comrade. As the story progresses, her crush could lead to some comical misunderstandings, like when she gets jealous of other girls around Naruto.
One possible plotline could be that they start as friends who gradually develop feelings for each other. But due to Anko's past or Naruto's status as a Jinchuriki, they decide to keep it a secret. Another could be that they are thrown together on a mission and during that time, they discover their love for each other but fear the reaction of others, especially Tsunade, so they keep it under wraps.