Perhaps in this fanfic, Naruto leaves Konoha because he wants to protect Sakura in his own way. He believes that his presence in the village is putting her in danger. So he decides to leave and draw the danger away from her. This could lead to a lot of self - discovery for Naruto and also some really emotional moments when Sakura realizes his true intentions.
In the fanfic, Naruto might leave Konoha because of the political situation in the village. He has always been an outsider in a way, being the Jinchuriki. With the Narusaku aspect, Sakura could be the reason he has held on for so long. But when things get too tough politically, he decides to leave. He then tries to build a new life outside the village, all while still having feelings for Sakura and wondering if she misses him too.
One possible plot could be that Naruto leaves Konoha due to some misunderstanding. Maybe he feels unappreciated in his relationship with Sakura (Narusaku). He might go on a journey to find himself. Along the way, he could encounter new enemies and also make new friends who help him see things from a different perspective.
His relationships with his friends like Sasuke and Kakashi would also be affected. Sasuke might understand Naruto's decision on some level, having also left the village before. Kakashi, on the other hand, would be worried about Naruto. He might try to find him and bring him back. This could create some tension between Naruto and Kakashi as Naruto tries to assert his independence.
In a 'Naruto Namikaze leaves Konoha' fanfic, it could be that Naruto is framed for a crime he didn't commit. The villagers turn against him, and even his friends start to doubt him. Feeling betrayed and alone, he decides to leave Konoha. As he travels, he meets other outcasts who have also been wrongly accused, and together they form a group to clear their names and seek justice.
In Shikanaru's fanfic, Naruto might leave Konoha because he feels restricted by the village's rules and traditions. He has always been a bit of an outcast, and leaving could be his way of finding true freedom. The story could follow his adventures in different lands, his attempts to build a new life, and his constant internal struggle between missing his old friends in Konoha and his newfound independence.
Maybe there are some dark secrets within Konoha that he discovers in the fanfic. These secrets could be related to the treatment of certain individuals or something more sinister about the village's leadership. Discovering such things could make Naruto decide to leave in order to distance himself from the corruption or unfairness.
Sakura would probably be very worried. She has always cared about Naruto deep down, so she might be constantly trying to find a way to bring him back. Kakashi, on the other hand, would likely understand Naruto's reasons to some extent. He might be sad but also respect Naruto's decision. As for Sasuke, if he is in the village at the time, he could be conflicted. He and Naruto have a complex relationship, and Naruto's leaving might make him realize how much Naruto actually means to him.
In this kind of fanfic, one possible scenario could be that Naruto leaves Konoha due to feeling misunderstood. Maybe he has been wrongly accused of something and decides that he can't stay in a place where people don't trust him.
It could be a rogue ninja from another village who has a vendetta against Naruto. This ninja might spread false rumors about Naruto in Konoha, which eventually leads to Naruto leaving. So, this ninja would be the main antagonist as he is the root cause of Naruto's departure.
In a 'naruto and kushina leaves konoha fanfic', perhaps they leave due to a threat to Naruto's safety that the village can't fully protect against. Maybe some secret organization is after him and they feel they have no choice but to go into hiding outside Konoha.
One idea could be that as Naruto leaves Konoha, he encounters a powerful and ancient creature in the wild. In a battle with it, the extreme stress and need to survive unlocks his hidden bloodline. This new power could be related to some kind of elemental control that is unique to his clan, like a special form of wind manipulation that is far more powerful than what he had before.
One possible reason could be for Naruto's safety. Maybe she has to go on a dangerous mission and believes Konoha is the safest place for him. Another reason might be that she is forced by some powerful enemies who threaten Naruto's life if she doesn't leave him in Konoha.