One possible fanfiction could be about Naruto's right arm gaining a new and mysterious power. Maybe it starts to glow with an unknown chakra, and he has to figure out how to control it without losing himself. It could be a power that has a connection to an ancient ninja clan's secret technique.
His right arm could get a cool tattoo that gives him extra powers. For instance, a tattoo that allows him to summon a special type of animal or use a unique jutsu.
One possible consequence could be a significant change in his fighting style. He might have to rely more on his left side and develop new jutsu techniques that can be executed with one arm. For example, he could focus on enhancing his Rasengan further to compensate for the loss of his right arm's abilities.
One possible storyline could be Naruto's struggle to adapt to his new physical state. He might have to relearn all his ninja techniques, now that he's missing an arm. For example, he'd have to find new ways to perform his signature Rasengan. Another could be his journey of self - acceptance, dealing with feelings of inadequacy compared to his former self. He could also face challenges from enemies who see his injury as a weakness and try to take advantage of it.
Sasuke could be a candidate. Given their complex relationship, Sasuke might find a way to give Naruto a new arm as a way to atone for their past differences. He could have discovered some rare medical ninjutsu during his travels or come across a powerful artifact that he uses to create a new arm for Naruto.
Another way his story could progress is that he becomes a symbol of resilience. Despite the loss of his arm, he continues to fight for his village and protect his loved ones. This could inspire the younger generation in the fanfiction, showing them that physical disabilities don't mean the end of one's capabilities.
Maybe Orochimaru. Despite being a villain in the past, he is a master of forbidden jutsus and experiments. He could see Naruto as an interesting subject and give him a new arm with some dark powers, which Naruto would then have to learn to control for the greater good.
Well, it could be that he got it as a gift from some super - advanced ninja technology group in the fanfiction world. Maybe they saw his need for an extra weapon or tool during battles and decided to equip him with a metal arm.
His combat abilities are severely affected. Naruto is known for his physical combat skills combined with his chakra - based attacks. Without his right arm, his punches and grappling moves are limited. He can't hold his kunai or shuriken as effectively in combat, which reduces his ranged attack options.
One special ability could be enhanced strength. The metal arm might be able to deliver much more powerful punches than his normal arm, allowing him to break through tough defenses more easily.