Naruto would need to train harder to make up for the lack of an arm. He could develop new jutsus or modify existing ones. Maybe he would start using more wind - based attacks that can be controlled with just one arm and his chakra control. Also, his friends might help him by creating prosthetics or assisting him in battles.
He might rely more on his other senses like hearing and smell. Just like real - world blind people can develop enhanced other senses, Naruto could use his chakra to sense the environment more acutely.
Well, Naruto might rely on his other senses more. His sense of smell, which is already quite sharp, could be enhanced further. He could also use his chakra to sense the environment around him, like how he can detect the presence of others. And he'd probably train with his friends more, especially those like Hinata who can guide him using her Byakugan.
He might start by training his aim constantly. Just like how he trained to be a ninja, he'd practice shooting at targets day in and day out.
There could be a plot where Naruto's friends are overly protective of him at first, but he has to convince them that he can still fight and be useful. Also, the story might focus on how Naruto's relationship with Sasuke changes. Sasuke might see Naruto in a new light and feel a new sense of respect for him because of how he copes with the loss of his arm.
Well, Naruto might first be really confused. He's used to being a boy, so suddenly being a girl would be a huge shock. He might start by trying to understand the physical differences. For example, getting used to different clothing styles. And in terms of his relationships, his friends like Sasuke might react in a strange way at first. But Naruto being Naruto, he'd probably still be as determined as ever. He could use this new form to his advantage in some situations, like using his new appearance to deceive enemies. After all, he has always been adaptable.
Well, Naruto might adapt to Shunpo in the fanfiction by first observing. He's good at that. He'd watch how others use it, break down the movements in his mind. Then he'd practice, using his determination. His chakra control, which he has improved over time, would also play a role. He'd likely infuse his own style into it, not just copy it blindly.
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.
Naruto may become more cautious. With a prosthetic arm, he realizes his vulnerability more. He might start to think more strategically before jumping into battles. For example, in a fight, he won't just rely on his brute strength but use the unique features of his prosthetic arm to his advantage.
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.
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.