It could be Sasuke. Maybe Sasuke is in a bad mood on Naruto's birthday and rejects Naruto's invitation to hang out or something. Since they have a complex relationship, Sasuke's rejection would really hit Naruto hard.
In this fanfiction, the villagers might reject Naruto. Even though he has done a lot for the village, there could still be some prejudice against him. On his birthday, when he expects to be more included, they could turn him away from a local event, which would be a big blow to him.
He might meet an old sage who has been living in seclusion near the village. The sage could see Naruto's loneliness on his birthday and offer him some ancient ninja knowledge.
In this kind of fanfiction, Naruto might feel extremely sad and lonely on his birthday. Maybe his friends forget his birthday, or he is rejected from a special event or by someone he cares about. It could lead to him reflecting on his relationships and his place in the village.
Sasuke could be one of the people who help him. Despite their past differences, they have a deep bond. Sasuke has his own skills and knowledge that could be useful in Naruto's situation, like his Sharingan abilities which could help in detecting enemies while Naruto is hiding his face.
He might meet other wandering ninjas who are also on a quest for power or knowledge. They could either become his allies or foes depending on their motives.
He would most likely meet his parents, Minato and Kushina.
Iruka - sensei could be one of those who help Naruto. He has always been like a father figure to Naruto and would offer emotional support. Rock Lee could also be a great helper. Lee, who has trained his body to be extremely powerful, could teach Naruto some physical combat techniques that don't rely on eyesight. And of course, the Nine - Tails inside Naruto might also play a role. It could potentially share some of its power or knowledge to help Naruto deal with his new situation.
Maybe Naruto would sell his soul to a dark and mysterious ninja who has some sort of ultimate power or knowledge. This ninja could be using Naruto's soul for some grand, but evil, plan.
He might show his scars to Sasuke. Given their complex relationship, it could be a powerful moment between them, a way to show Sasuke that Naruto has also faced great pain in their separation and the events that followed.
In this fanfiction, Naruto could reject his clan because of the dark secrets or past actions of the clan. He is a character who values justice and friendship. If the clan has a history of wrongdoings that he discovers, he may not want to be associated with it. Also, Naruto has his own dreams and goals that might not fit within the framework of the clan. He has always been a bit of a rebel, and rejecting the clan could be his way of standing up for what he believes in.
One possible reason could be a long - held misunderstanding. Maybe Naruto discovers some family secrets that he misinterprets as betrayal or neglect. For example, if he finds out that his family had made some sort of pact that he disagrees with, it could lead to his rejection.