It could also be that in this fanfic, Naruto's arm is lost as a result of some sort of dark magic or curse. Perhaps he was exploring an ancient and dangerous place and unknowingly triggered a curse that cost him his arm, which would then lead to him having to find a way to overcome this new handicap and continue his journey as a ninja.
Another scenario might be that Naruto sacrifices his arm to save someone he cares about deeply. He might have used his arm to block a fatal attack aimed at a friend or a loved one, showing his selfless nature even in a fan - created story.
One possible scenario could be Naruto having to relearn his ninja skills with only one arm. He might struggle at first but then find new ways to perform jutsus. For example, he could modify his Rasengan technique to be more one - handed friendly.
Perhaps in the fanfic, Naruto loses his arm due to a curse or a forbidden jutsu gone wrong. His friends, like Sasuke, then try to find a way to either get him a new arm or help him come to terms with the loss. It could also show Naruto's journey to adapt to his new disability and still be a great ninja, inspiring the younger generation in the process.
In the context of the fanfic, it could also impact his relationships. His friends might be overly protective, which Naruto may not like. Or, he could inspire others with his determination to keep going despite his injury. It might also change how he is perceived in the ninja world. Some may see him as weakened, while others could view him as even more of a hero for his ability to persevere.
Naruto might become more cautious. Losing an arm would make him realize his vulnerability more. He would probably be more strategic in battles, relying less on brute force and more on his intelligence and remaining ninja skills.
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.
One possible plot could be Naruto losing his arm during a battle with a powerful new enemy. He then has to struggle with not only the physical loss but also the emotional and mental toll it takes on him as a ninja. He might have to learn new fighting techniques that don't rely on two arms.
One scenario might be related to a failed mission. Maybe Naruto is sent on a top - secret mission that is much more dangerous than anyone anticipated. He could be betrayed by someone he trusts during the mission, leading to his death. Or perhaps there are some unforeseen circumstances, like a strange and deadly curse that gets unleashed during the mission which he succumbs to.
Perhaps in the fanfic, there is a prophecy that says Naruto's friends will be the cause of his downfall. So, Naruto, fearing for his future and the safety of the village, starts to distance himself from them and eventually hates them. Or maybe his friends accidentally cause the death of someone Naruto loves dearly, which makes him unable to forgive them.
Maybe Naruto gives up because he faces too much criticism in the fanfic world. He might feel that he can't meet the high expectations of the fans.
One possible scenario could be Naruto being constantly ostracized in the village. People might avoid him not just because of the Nine - Tails inside him, but also due to false rumors spread about him. For example, they could say he's a bad omen. This would lead to Naruto feeling extremely lonely and isolated, and he might start to train alone more often, distancing himself further from the possibility of making friends.