He might wish for the end of all hatred in the ninja world. This would mean no more wars and grudges among the villages. Everyone could focus on building a better future together.
If he wishes for peace, the entire political structure of the ninja world would change. There would be no need for the hidden villages to constantly be on guard against each other. This could lead to a more unified ninja world where resources are shared, and everyone can progress together.
First, understand the characters well. Know Itachi's backstory, his motives, and his relationships. For example, his loyalty to the village and his love for Sasuke. Then, think about what kind of wish he might have as an adult. It could be something related to atoning for his past sins or protecting those he loves. Start with a strong opening that sets the mood and the premise of the story. Maybe start with Itachi in a moment of reflection.
One interesting aspect could be stories where Itachi wishes for peace in the ninja world in a more adult and complex way. For example, he might use his skills and knowledge to broker treaties between warring clans. In some fanfictions, his wish could be to see Sasuke grow into a strong and wise ninja without the burden of revenge. This often involves Itachi making sacrifices behind the scenes to ensure Sasuke's development.
Another possibility for Itachi's last wish could be the restoration of the Uchiha clan's honor. He dedicated his life to protecting the village, which led to the downfall of his clan. So, perhaps in fanfiction, he wishes for a way to reconcile the village and the remaining Uchiha members, allowing them to once again be respected within Konoha.
It could be a fanfic where a character in Naruto wishes another great happiness. Maybe Naruto himself wishes Sasuke happiness after all their struggles. It might explore the deep bonds between characters and how one's well - being affects others in the Naruto universe.
There's also 'Brothers in Battle: Naruto and Konohamaru'. This fanfic focuses on Naruto taking Konohamaru under his wing in a more brotherly way. It's full of action as they face various threats together and Naruto imparts his wisdom and skills to Konohamaru, just like an older brother would. It's a heartwarming take on the idea of brotherhood in the Naruto universe.
If you want to read a Naruto novel with an invincible main character and a wishing system, then I recommend you to read " Naruto: Uchiha Ape Flies "! Transmigrating to the home of the Yuan Fei clan, the protagonist possesses the Shurunyan and the ability to replicate, reversing the fate of the Uchiha clan and becoming the strongest ninja. This book doesn't have any external power system. It's considered a pure Naruto Doujinshi, and it doesn't have a copying function. I hope you like my recommendation. Muah!
One of the most exciting wishes could be bringing back his parents. Imagine Naruto growing up with Minato and Kushina. He would finally have the family he always longed for. They could teach him more about the Uzumaki clan and their powers, and Naruto would have a much different and perhaps more stable upbringing. It would also be a chance for Minato to see how his son has grown and surpassed him in many ways.