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.
Maybe Naruto's right arm is cursed in fanfiction. It could be that an evil ninja placed a curse on it, and Naruto has to go on a journey to find a way to break the curse. Along the way, he meets different characters who either try to help or hinder him in his quest.
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.
Well, perhaps the new arm comes from some kind of ancient and mysterious source. It could be an arm that was once part of a powerful ninja from the past. This new arm could have a mind of its own, at first causing Naruto some trouble as he tries to control it, but eventually they work in harmony and it gives Naruto an edge in battles against tough enemies.
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.
There could be epic battles. Maybe Naruto's right - hand has to fight against powerful enemies who are trying to undermine Naruto's rule as Hokage. They would use their skills and teamwork to defeat these foes.
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.
Immediately after, they could share a knowing look and then rush off to face a new threat. Their combined energy from the fist bump gives them an extra boost.
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, one possibility could be that Naruto gets a new arm with some special abilities. Maybe it was given to him by a powerful ally or he discovers an ancient artifact that attaches to him as a new arm. This new arm could have powers like enhanced strength for his ninja techniques or the ability to sense danger more acutely.
One possibility is that in this fanfiction, Scabior has an ulterior motive for putting his arm around Hermione's waist. Maybe he's trying to use her to get to Harry Potter. He could be pretending to be friendly while secretly plotting. However, Hermione being the intelligent witch she is, might be aware of his true intentions and be planning her own counter - move.
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.