Well, from a practical standpoint, comparing the two is like comparing apples and oranges. Their universes have different rules regarding power and physics. In a fanfic, though, the writer can manipulate the story to suit their desired outcome. Maybe Naruto uses his intelligence and strategic thinking along with his chakra powers to defeat Superman. It could be that the fanfic has Superman in a situation where his powers are nullified and Naruto is able to use his ninja skills to gain the upper hand.
Well, first of all, Naruto could use his ability to sense chakra to find Superman's weak points. Once he locates them, he could use his wind - style jutsu, like the Rasenshuriken, which is a powerful and cutting - edge attack. He could also use his teleportation - like jutsu, the Flying Thunder God Technique, to quickly get behind Superman and attack him from a blind spot. Superman might try to use his heat vision, but Naruto could use his chakra shield to block it. And if the fanfic allows, Naruto could even gain some new power during the battle, like the power to nullify Superman's super strength, and then land a final, decisive blow.
In the fanfic, it could start with a build - up of tension between Naruto and Sasuke. Naruto has been training hard and has reached a new level of power. Sasuke, on the other hand, might be underestimating Naruto. When they finally clash, Naruto's sheer determination and his unique Uzumaki chakra, along with his mastery over the Nine - Tails' power, allow him to dominate the fight and kick Sasuke's ass. This could also be a way for Naruto to try and bring Sasuke back to the village, by showing him that he can't always have his way and that they are stronger together.
One interesting way could be through the use of genjutsu. Naruto could trap Superman in an illusion where he believes he has lost his powers or is facing an unbeatable foe. Since Superman's mind is not immune to such psychic attacks in a fan - created scenario, Naruto could then use his physical attacks like Rasengan to finish him off.
Often, it's powerful villains like Orochimaru who make a comeback in fanfiction. Naruto has to use his growth and new abilities to defeat him once and for all.
It depends. Some fans might find it acceptable as it could explore different character dynamics and power relationships. They might see it as a creative take on the characters.
In such a fanfiction, perhaps Naruto has been pushed too far by Sakura's constant nagging. He might finally snap and show his superior combat skills. Maybe Sakura made a wrong decision during a mission that endangered the whole team, and Naruto, in his fury, decides to teach her a lesson through a non - lethal fight.
Well, in some of these fanfictions, Naruto might show off new and powerful jutsu that he didn't have in the original series. For example, he could combine his Rasengan with some kind of elemental power in a really cool way.