In a straight - up fight, Itachi has some very powerful abilities. His genjutsu can be extremely difficult to break out of, and his ninjutsu attacks are strong. But Batman is no slouch. He has fought against some of the most powerful villains in the DC universe. He would study Itachi's moves and try to find a pattern. Batman might also use his wealth to create some sort of countermeasure to Itachi's Sharingan. Overall, it's a very close call and would likely depend on how the writer of the fanfiction wants the story to go.
One interesting scenario could be a battle in a dark, abandoned cityscape. Itachi's Sharingan abilities would give him an edge in terms of perception and illusions. Batman, on the other hand, would rely on his gadgets and combat skills. He might use smoke bombs to disrupt Itachi's line of sight and then try to get in close with his martial arts. Another scenario could be a mental battle. Itachi is used to psychological warfare, but Batman is also a master of getting into his opponents' heads. Itachi might try to use his genjutsu to break Batman's will, but Batman's strong mental discipline could resist it.
One interesting scenario could be a battle of wits. Itachi is known for his intelligence and Sakura has grown to be a very smart and capable ninja. They might engage in a mental duel where they try to outmaneuver each other with strategic moves and mind games.
Toge Inumaki is important too. His special cursed speech ability makes him stand out. Also, the principal of the school, Masamichi Yaga, is likely to be important as he is in a position of authority and has an influence on Gojo and the other students. There could be other characters like the members of different clans that also play roles in the complex web of the story.
In most traditional interpretations, Itachi would be favored to win due to his long - established reputation as a powerful and feared ninja. But in the realm of fanfiction, the writer can tip the scales in Sakura's favor. For example, if Sakura has mastered some sort of anti - Sharingan technique or has a power - up that nullifies Itachi's main abilities, she could emerge victorious.
I think young Sasuke would have a very intense reaction. He was so consumed by his hatred for Itachi at that young age. A Sasuke vs Itachi fanfiction would be like a trigger for him. He would be eager to see how the fictional fight is portrayed. If Sasuke in the fanfiction is shown as strong, it might fuel his own ego and make him strive even harder to become powerful. However, if the fanfiction shows Itachi as superior, it could enrage him. He might feel that it undermines his own goal of defeating Itachi and he might even want to find the writer to correct their 'wrong' view.