In a fanfic, there could be a scenario where Naruto and Superman start off as enemies but then realize they have a common enemy. They then team up against this new threat. During their initial fight, Superman might underestimate Naruto's speed and agility, which are enhanced by his ninja training. Naruto, on the other hand, might be initially shocked by Superman's sheer power. But as the fight progresses, they could come to respect each other's abilities and decide to work together.
One scenario could be that Naruto uses his shadow clone jutsu to overwhelm Superman. The clones could attack from all directions, and while Superman is busy dealing with them, Naruto could prepare a powerful Rasengan. Another scenario might be Superman using his heat vision to try and stop Naruto's summons, like the giant toads. But Naruto could use his speed and agility to dodge and counter - attack.
In a fanfic, Naruto might power up by having a spiritual awakening. He could connect with the spirits of past Hokages in a deeper way, gaining their knowledge and some of their power. This could enhance his existing jutsu and give him new abilities. Vegeta could power up if he were to face a near - death experience against Naruto. This could trigger a hidden potential within him, like a new type of Super Saiyan form that has unique abilities. He could also fuse with another Saiyan (if there were another Saiyan available in the fanfic's scenario) to create an even more powerful being.
Another scenario could be that Naruto and Sasuke discover a new power within themselves during the fight against Kaguya. This new power could be related to their friendship or their connection to the Sage of Six Paths. They then use this power to finally defeat Kaguya.
In a fanfiction battle, perhaps the fight begins with Naruto trying to talk to Goku first, to understand his intentions. Goku, not really understanding Naruto's world, just wants to test his strength. So he attacks without warning. Naruto quickly enters his Nine - Tails Chakra Mode to defend himself. The fight then escalates as Goku powers up further. The two exchange blows, with Goku's punches creating shockwaves and Naruto's attacks leaving marks on the ground. As the fight goes on, they both start to respect each other's power and skills, and it becomes more of a battle of wits as well as strength.
One scenario could be Naruto using his clones to distract the Justice League while he sneaks up on Superman and uses a powerful jutsu. Another could be the Justice League trying to find Naruto's weakness, like his connection to the nine - tailed fox, and Naruto having to defend himself against their attacks. Maybe Batman tries to analyze Naruto's fighting style and come up with a plan to defeat him.
One scenario might be related to a failed mission. Maybe Naruto is sent on a top - secret mission that is much more dangerous than anyone anticipated. He could be betrayed by someone he trusts during the mission, leading to his death. Or perhaps there are some unforeseen circumstances, like a strange and deadly curse that gets unleashed during the mission which he succumbs to.
Well, perhaps in the fanfic, Naruto has to team up with his friends in a unique way to seal the Juubi. For example, Sasuke could use his Sharingan to help Naruto locate the weak points of the Juubi while Naruto does the actual sealing. And Sakura could use her medical ninjutsu to keep Naruto in top shape during the process.
One possible storyline could be that Thanos arrives on Earth seeking a powerful artifact. Superman steps in to stop him. They battle it out across the city, with Superman using his strength and speed to try and take down Thanos. Another could be that Thanos somehow manages to get Superman under his control using the Infinity Stones, and then the rest of the Justice League has to figure out how to free Superman and defeat Thanos.
One scenario could be that Naruto discovers some hidden secrets about Minato and Kushina that he interprets as them being selfish. For instance, he might find out that they had a choice to be with him but chose something else instead, which makes him angry and full of hatred towards them.
One possible scenario could be in a fanfic where Sakura accidentally uses her strength during a training session with Naruto and physically hurts him. Maybe she misjudges her punch or kick.