There are indeed alternatives. Some fanfics might explore the relationships between Naruto and other characters in the Blood Prison context. For example, they could depict how Naruto interacts with the guards or other prisoners in a way that promotes the values of the Naruto universe, such as perseverance, loyalty, and friendship. It's important to avoid the offensive ones and seek out the positive fan - created stories.
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.
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.
In this type of fanfiction, the plot can be really diverse. It might start with Naruto being sent to the Blood Prison for some false accusations. Once there, he encounters various characters, some of whom are trying to kill him, while others might become his allies. The Blood Prison setting allows for a lot of exploration of Naruto's character in a darker context. It could also involve Naruto having to use his skills in new and creative ways to survive, and perhaps there's a build - up to a big showdown against the main villain or the corrupt forces running the prison.
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.
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.
I haven't read this particular fanfic in detail. But generally, in fanfics about Naruto in the Blood Prison, his changes could involve his growth in power, his relationships with other characters in that unique and often dangerous setting. Maybe he discovers new jutsu or overcomes some inner demons while locked up there.
In the 'Naruto betrayed blood prison fanfiction', perhaps Naruto is betrayed first by someone he trusts inside the prison. This betrayal makes him take actions that are misinterpreted as him turning on the prison. It might also be that a new, powerful inmate arrives and manages to turn the situation around so that Naruto looks like the bad guy. He could be forced to fight against the prison guards to protect himself or others, which would be seen as betrayal.
Sakura could use her medical ninjutsu to heal Naruto if he gets injured during the escape and also use her strength to fight off guards. She might also have some knowledge about the prison from her studies.
The main character is Naruto, as it's a Naruto - centered fanfiction. But in the Blood Prison setting, there could be other key characters. For example, the warden of the prison who might be a cruel or mysterious figure. Also, there could be a fellow inmate who has a special connection with Naruto, either as a friend or a rival. These characters play important roles in driving the story forward in the context of the dark and dangerous Blood Prison.