One idea could be that Kurama is trapped in a special jail within Naruto's mind. Maybe it's a result of some dark magic or a side effect of a new jutsu Naruto attempts. In the fanfiction, Naruto could be desperately trying to find a way to free Kurama while also dealing with the internal chaos that Kurama's imprisonment causes within him.
Maybe Naruto breaks out of a prison in a hidden village where he was wrongly imprisoned. He then has to evade capture while trying to prove his innocence.
Naruto himself could be in jail fanfiction. Maybe he was framed for a crime he didn't commit and has to prove his innocence from within the prison. Sasuke is also a likely candidate. His brooding and sometimes anti - social nature could lead to him getting into trouble with the law in a fanfiction setting. Another one could be Orochimaru. Given his history of unethical experiments, it's not hard to imagine him ending up in jail in a fan - created scenario.
In Naruto jail fanfiction, the exploration of forbidden jutsus could be a great concept. Some inmates might be in jail because they were caught using or researching dangerous or forbidden jutsus. Naruto, being curious, could get involved in trying to understand these jutsus while also trying to prevent them from being misused further. It could lead to a whole new set of adventures and challenges for him inside the prison.
Well, it's a fan - created story related to Naruto. The 'limbo border jail' is likely a made - up or very niche concept within the Naruto fan world. It could involve Naruto or other characters facing new challenges in this jail. Maybe it's a place where villains are sent, and a story could revolve around a character trying to break someone out or deal with the chaos inside the jail.
Well, perhaps Naruto accidentally breaks a really important and ancient law in the ninja world. It could be something related to a forbidden jutsu that he was unknowingly involved in. As a result, he's thrown into jail. There, he might start to reflect on his actions and ninja way, and also try to find a way to prove his innocence while making some unexpected allies among the prisoners.
Kurama might start to lose his power in Naruto's jail. Since he's confined, his connection to the natural chakra sources could be severed, causing him to weaken gradually. Naruto would then have to find a way to restore that connection, perhaps by finding a hidden key within his own memories that unlocks the jail and restores Kurama's power.
In this 'Naruto released from jail' fanfiction, it could be that Naruto was jailed because of some false accusations related to a powerful and dangerous jutsu he was suspected of misusing. After his release, he embarks on a journey to find the real source of the jutsu and prove that it can be used for good. Along the way, he meets new allies and old enemies, and has to use his wits and strength to overcome various obstacles.
Perhaps Naruto ends up in jail due to some political conspiracy in the ninja world. While in jail, he discovers a secret underground network that is planning something big that could endanger the whole ninja world. He then has to use his skills and wits to stop it from inside the jail, all while dealing with the harsh conditions and difficult inmates.