Well, in some fanfictions, he might get it from a skilled ninja prosthetics maker. This maker could be someone who specializes in creating artificial limbs for ninjas who have lost their arms in battle.
One common theme is adaptation. Naruto has to adapt to having a fake arm, whether it's in combat, training, or daily life. Another theme is often power - up. The fake arm might give him new abilities or enhance his existing ones. For example, it could be a super - strong arm made of some rare material that lets him punch through walls or something.
It could have enhanced strength. Since Naruto is already quite strong, the fake arm might be designed in the fanfiction to multiply his physical power, allowing him to punch even harder or hold heavier objects.
One interesting Naruto fake arm fanfiction could be one where Naruto gets a special prosthetic arm after a battle. It might have unique abilities, like being able to channel chakra in new ways. Maybe it was crafted by a hidden master. Another could focus on how he adjusts to having a fake arm in his daily ninja life, dealing with tasks that were once easy but now are a challenge.
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.
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.
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.
One common theme is resilience. Naruto having one arm is a major setback, but in these fanfictions, he always bounces back. For instance, he might struggle at first but then finds ways to be as strong as before.
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.