In a 'naruto goes to prison' fanfiction, it could be that Naruto is tricked into taking the blame for someone else. Once in prison, he meets old foes who are also incarcerated. Instead of fighting them, he tries to understand their motives and in the process, he uncovers secrets about their pasts that were related to some greater threat to the ninja world. This knowledge then becomes crucial for his future actions outside the prison.
The plot could involve Naruto being sent to the Blood Prison on a mission. Once inside, he encounters various types of ninjas with different abilities and motives. There could be a mystery surrounding a powerful and dangerous prisoner locked away deep within the prison. Naruto's journey in the Blood Prison could also be a test of his character, as he has to make difficult decisions about who to trust and how to handle the dangerous situations that keep arising. He may even learn some new jutsu from the inmates or discover a hidden power within the prison itself.
It could be a corrupt ninja from another village who wants to get rid of Naruto as he sees him as a threat to his own plans. This ninja could have framed Naruto to send him to prison.
In this fanfiction, Naruto will surely interact with his friends who might be trying to break him out or at least communicate with him from the outside. Inside the prison, he'll encounter inmates with diverse personalities. There could be a wise old prisoner who imparts some valuable wisdom to Naruto. Also, there may be a group of inmates who form a sort of gang within the prison, and Naruto has to either fight them or make peace with them depending on the situation. And of course, there could be a mysterious figure who seems to know more about Naruto's presence in the prison than he himself does, and Naruto will have to figure out this person's motives and identity.
One possible plot could be that Naruto is framed for a crime he didn't commit. Maybe someone with a vendetta against him plants false evidence. In prison, he would have to deal with tough inmates and the strict prison regime while trying to prove his innocence.
Maybe Danzo could be the main antagonist. He has always been a bit of a shady character in the Naruto series. He could see Naruto as a threat and use his influence to frame him and send him to prison to further his own political or power - hungry goals.
Well, one possibility could be that Percy is framed for a crime he didn't commit. Maybe some powerful enemy uses magic or trickery to make it seem like he's violated a major demigod law. So, he's sent to a special prison for demigods. Inside, he has to deal with all sorts of other dangerous inmates, some of whom might be old enemies or just generally bad - tempered demigods. He'd probably try to find a way to prove his innocence and escape while also having to survive the various challenges within the prison.
He could use his transformation jutsu. He could transform into a guard or an inmate who has access to the prison exit areas. Then he could just walk out when the opportunity arises.
There could be an ancient and evil force that has infiltrated the demigod world. This force uses Percy as a scapegoat and arranges for him to be sent to prison. It wants to cause chaos and destruction within the demigod community. It manipulates the situation from the shadows, and Percy has to figure out its identity and motives while in prison in order to stop it.
If Naruto goes to Wakanda, he could potentially form new alliances. His friendly nature might lead him to make friends with the Wakandan warriors. He could learn about their unique fighting styles and in return, teach them some ninja techniques. It would be an interesting exchange of skills and knowledge.