One possible reason could be a major betrayal. Maybe someone he trusted deeply, like a close friend or a mentor, turned against him. This would make him lose faith in people and become cold as a form of self - protection.
It could also be due to the loss of too many people he cared about. If he witnessed the deaths of his friends one after another in battles, he might become distant as a way to avoid the pain of future losses. He would start to keep people at a distance so that he wouldn't get hurt again.
One possible reason could be a major betrayal he experienced. Maybe someone he trusted deeply, like a close friend or a mentor, turned against him. This would make him more guarded and distant to avoid getting hurt again.
One possible reason could be a great betrayal. Maybe he discovers that someone he deeply trusted, like a close friend or a respected mentor, has been using him all along. This would shatter his trust and make him withdraw from people, thus becoming cold.
One reason could be a great loss. Maybe he lost someone really important like Jiraiya in a more tragic way that made him shut down. Another could be that he discovered some dark secret about the village that made him lose faith in everyone.
One reason could be to explore a different side of Naruto's character. In the original series, he's so warm - hearted, but by making him cold and distant, the writer can show how different events could have shaped him in an alternate way. Maybe he faced more hardships or betrayals that led to this change.
His relationship with Sakura would definitely be affected. Sakura, who has always known the warm - hearted Naruto, would be shocked and confused. She might try to reach out to him at first, but if he keeps pushing her away, she could become frustrated or even give up. Their friendship would be strained.
Perhaps he is trying to distance himself from his past self. Naruto has had a tough childhood and has been through a lot. Changing his appearance could be a way for him to start anew, to shed the image of the 'troublemaker' or the 'lonely kid'. He might want to present a new, more confident and respected image to the people around him, both friends and foes.
One possible reason could be a feeling of betrayal. Maybe he found out some long - hidden family secrets that made him lose trust in his family. For example, if he discovered that his parents had made a deal with some dark force in the past that had negative consequences for him or the village.
One possible reason could be that he has faced a lot of misunderstandings within the family. Maybe his family has certain expectations that he can't meet, and over time, this has led to his coldness. For example, if his family doesn't understand his dreams or ambitions, Naruto might feel alienated.
It could be due to a new jutsu he's trying to master that has some side effects on his emotions. Maybe it's a powerful ice - based jutsu that's making him cold in nature as well.
Perhaps he has trust issues. He might have been betrayed in the past, so now he keeps everyone at a distance to avoid getting hurt again.