One common reason is love. If Naruto falls in love in a fanfiction, he may become more gentle and considerate, changing his usually rambunctious attitude. His focus could shift from just being the best ninja to also taking care of the person he loves.
Well, sometimes in fanfiction, Naruto changes his attitude when he discovers a new power within himself. Realizing that this power comes with great responsibility, he could become more solemn and focused. He might start to view his friends and enemies in a different light, perhaps seeing the potential for good in his foes and being more cautious about involving his friends in dangerous situations.
In some fanfictions, Naruto might change his attitude due to a major event. For example, if he fails to protect a dear friend, he could become more serious and less impulsive. This new attitude would be a result of the guilt and the realization of his own limitations.
One possible reason could be that Naruto has grown so much on his own journey. He has faced numerous challenges and made many friends who have become like family to him. So, in a sense, he feels self - sufficient and no longer feels the acute need for his absent parents.
One possible reason could be that Naruto is so used to being on his own and having his own independent life. He has grown up without a traditional family for a long time, and the idea of suddenly having a family might seem very foreign and restrictive to him. He might fear losing his freedom and the self - made identity he has created over the years.
It could also be due to a prophecy or some sort of spiritual guidance. In the Naruto universe, there are often prophecies that guide the characters' actions. A prophecy might suggest that changing his name would bring about some great change or power. For instance, if there was a prophecy that a new name would help him unlock a hidden power or unite different ninja clans under a new banner.
It could also be due to some sort of mind - control or curse. In the Naruto universe, there are many powerful jutsus and dark magics. Perhaps an enemy has cast a spell on him that makes him not care about his own life. This would be a dangerous situation as he could be easily manipulated into dangerous situations without self - preservation.
Another reason could be a personal journey of self - discovery. Naruto might feel that his identity as the hero of the village has become a burden or a limiting factor in his growth. Changing his identity could allow him to explore new aspects of himself, away from the expectations and responsibilities that come with being Naruto Uzumaki.
Perhaps in the fanfic, Naruto is trying to fit into a different group or culture. His original hair style might make him stand out in a negative way in that context, so he changes it to be more accepted. Or it could be part of a bet or a challenge. For instance, he loses a bet with his friends and as a consequence, he has to change his hair style.
One reason could be jealousy. Maybe Naruto's success as a ninja makes his girlfriend jealous and she betrays him out of spite. Another reason might be that she is forced to by an enemy. For example, if she is blackmailed into betraying Naruto to save her family.
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.