It really depends on the writer's perspective. Some might have Naruto win because of his unwavering belief in friendship and his ability to draw strength from those around him. His large pool of chakra and his various powerful jutsu could give him the upper hand.
For Naruto, he might become more determined to bring Sasuke back to the right path. The fight in the bathroom could be a turning point where he realizes that he can't just use words but also has to show his strength. Sasuke, on the other hand, could start to question his own motives a bit more. Maybe seeing Naruto's unwavering spirit in such a strange setting makes him think twice about his actions.
One interesting scenario could be that Naruto and Sasuke discover a new power within themselves during the fight that changes the whole dynamic. Maybe Naruto unlocks a new form of Sage Mode that gives him an edge, and Sasuke responds with a new sharingan evolution.
Naruto often has his Nine - Tails chakra at his disposal. This gives him a huge boost in strength, speed, and endurance. He can also use his Rasengan, which is a highly concentrated ball of chakra. Sasuke, on the other hand, has his Sharingan, which allows him to predict his opponent's moves and copy some jutsus. He also has his Chidori, a powerful lightning - based attack. So Naruto's power is more about raw strength and stamina from the Nine - Tails, while Sasuke's is more about precision and speed with his Sharingan and Chidori.
In a great Naruto Sasuke fight fanfic, the moment right before they reach their physical limits can be extremely intense. Their bodies are bruised and battered, but their eyes still burn with a fierce determination. They've been at it for what seems like hours, and the battle has taken them through various terrains, destroying everything in their path. At this point, they both know that the next move could be the decisive one. Naruto, with his unwavering belief in friendship, and Sasuke, with his thirst for power and revenge, are at a standstill, but the tension in the air is palpable, like a storm about to break.
One reason could be Naruto's power. In the Naruto universe, Naruto has great power, and both Itachi and Sasuke might see Naruto as a key to achieving certain goals. Itachi might want to protect Naruto because he sees Naruto as a force for good in the future of the ninja world. Sasuke, on the other hand, may view Naruto as a rival in terms of power and influence, and in fanfiction, this could lead to a fight between them over Naruto.
Their relationships could develop in a more positive way. Through fighting together, they start to understand each other better. Naruto and Sasuke might finally put aside their old rivalries completely. Sakura could gain more respect from both of them as she shows her strength and intelligence in battle.
Well, Boruto might feel a sense of pride seeing his father Naruto in action against Sasuke. He has heard so many stories about their battles, and now seeing it in a fanfiction version could make him realize the deep bond and rivalry between them. He might also analyze their fighting styles and try to incorporate some of their moves into his own combat techniques later on.
Itachi. He was a highly skilled and intelligent shinobi. His Sharingan abilities were extremely powerful, and he had a lot of combat experience. He also had a strategic mind, which would give him an edge in a fight over Naruto.