It could be due to a misunderstanding or false identity. Maybe there is a character who looks similar to Naruto's heir and they are using the name for their own gain. Or it could be a case of identity theft within the context of the fanfiction world. Another aspect could be that the person taking the name has some sort of vendetta against Naruto and wants to use his heir's name to cause him emotional pain.
One possible reason could be a plot by an enemy to undermine Naruto's legacy. By taking the heir name, they can create confusion and disrupt the line of succession in Konoha. It might also be part of a political maneuver within the village, where some faction wants to gain control over Naruto's influence through his heir's name.
Perhaps it's a result of a curse or a dark prophecy. In some fanfictions, there are often such elements. The name being taken could be a sign that something bad is about to happen to Naruto's family or the village as a whole. It could also be that someone believes that by taking the name, they can gain the power or abilities that are associated with Naruto's line.
One possible reason could be political intrigue within the village. Maybe there are factions that don't want Naruto to have the heir name because they fear his growing influence. Another reason might be related to some hidden secrets about his family that are being unearthed, causing the village elders to question his suitability for the heir name.
Perhaps Naruto's parents were cursed or had some sort of premonition about a great danger coming to Naruto if he stayed with them. They believed that by separating from him, he would have a better chance of survival. Fanfiction writers often explore these kinds of emotional and complex scenarios to give a different perspective on Naruto's origin.
He might be really angry at first. Naruto has always fought for recognition, and having the heir name taken away would feel like a huge slap in the face. So he could lash out, trying to prove his worth.
One possible reason could be as a form of humiliation. His enemies might take his glasses to make him feel vulnerable and less in control. Without his glasses, Harry is severely visually impaired, so it's a way to undermine his confidence.
One possible reason could be that Naruto was taken for his special chakra. In the Naruto universe, his chakra is unique as he is the jinchuriki of the Nine - Tails. Some evil forces might want to control or study his chakra, so they take him from his parents. Another reason could be related to a prophecy. Maybe there are those who believe Naruto will bring great change, either good or bad according to their perspective, and they take him to try and influence his future.
It could be a misunderstanding. Perhaps Naruto was involved in an incident where his actions were misinterpreted by his brother. For example, Naruto might have accidentally caused harm to someone his brother cared about while trying to do something good, and his brother didn't get the full story and started to hate him as a result.
Maybe he just wants a new look. Naruto is always known for his wild and adventurous spirit, so dyeing his hair red could be a way to show his rebellious side or simply to stand out more.
In this fanfiction, it could be that Naruto's parents were under some sort of mind - control. Some evil entity could have taken over their minds and made them feel hatred towards Naruto. Also, it might be related to a family secret or feud. There could be something in the family's past that made them believe Naruto was a stain on their family name, even though Naruto himself was innocent. It could also be a case of false information being spread around the village which made his parents believe lies about him.
One possible reason could be that Naruto feels abandoned. His father was not around during his childhood, and he had to face a lot of hardships alone. Growing up without a father figure, he might have developed resentment.
One possible reason could be a plot by some dark forces to gain an advantage over Harry. Maybe they thought by separating him from his father, they could manipulate him more easily later on. Another reason might be related to some ancient prophecy. In the wizarding world, prophecies often drive actions, and perhaps this was seen as a necessary step to either protect or use Harry in relation to the prophecy.