Maybe Naruto has discovered something about Sakura that goes against his values. His arm could be a physical manifestation of his strength and determination to confront her about it. For example, if Sakura was involved in something unethical in the fanfiction, Naruto's confrontation through his arm could be a way to set things straight.
The reason could be related to a misunderstanding. Naruto's arm might have a special significance in the story, like it was injured while protecting Sakura from something she didn't fully understand. So he confronts her using his arm to show her the physical and emotional toll it took on him, and to clear up the misunderstanding between them.
In this fanfiction scenario, Naruto confronting Sakura in his arm could lead to a moment of self - discovery for Sakura. She might realize how much Naruto has grown and changed, and that she has been misjudging him all along. This could be the start of a new chapter in their relationship, where Sakura starts to see Naruto in a new light and they become closer as friends or even something more.
It could be related to a mission. Suppose Naruto's arm has some special power or ability that is crucial for a mission, but Sakura disagrees with how Naruto is using or handling it, thus causing the confrontation.
In the long run, this confrontation could be a turning point. If they overcome their differences, it could lead to a deeper and more mature relationship. For example, they might start to respect each other's views more and work together more effectively in future adventures.
One possible plot could be Naruto finding Sakura physically injured after a battle with a powerful enemy. He might confront her about her recklessness in battle, but also show his deep concern for her well - being. For example, Naruto could scold Sakura for not waiting for backup, while at the same time using his own chakra to heal her wounds.
Maybe he was protecting someone in Wave. He's always the self - sacrificing type, so he could have put himself in harm's way to save a villager or a friend.
Another possibility is that Naruto and Yang have a special bond. This bond could be formed through shared experiences, like they both went through a difficult training together or survived a life - threatening situation. Because of this special connection, Naruto feels indebted to Yang or simply values Yang's life more than his own arm.
One possible scenario could be Naruto confronting Hinata about her overprotectiveness. He might feel that she's being too clingy and it's affecting his freedom to pursue his ninja duties.
One possible reason could be her long - standing and deep - rooted love for Sasuke. Since childhood, she has had strong feelings for him. Maybe in this fanfiction, she realizes that her feelings for Sasuke are unshakable and that she can't continue to be with Naruto while having such intense feelings for another.
Maybe he starts to train with one - armed techniques. He could learn from other one - armed ninjas if there are any in the fanfiction world. His friends would also play a big role. They might encourage him to keep going or help him in his training.
Perhaps he meets an ancient sage or a hermit who has the knowledge of regeneration. This character could guide Shino and provide him with the necessary herbs, incantations or mental exercises to regrow his arm. It could be a spiritual journey for Shino as he has to prove himself worthy to receive this knowledge.