Perhaps Percy is in jail as a sacrifice for someone he loves. In the fanfiction, he might be accepting his situation at first, but then his friends outside start to plan a rescue mission. It could show his loyalty and their determination to get him out.
It could be that Percy committed a crime in a fit of rage or to protect someone, and now he has to face the consequences in jail. The fanfiction might explore his internal conflict, his remorse if any, and how he tries to make amends even from behind bars.
One possible plot could be that Edward is wrongly accused and is in jail. His friends outside start an investigation to prove his innocence. They might face many obstacles like uncooperative witnesses or a corrupt system.
It could be that Batman breaks one of his own moral codes in a desperate situation. For example, he might accidentally cause the death of a criminal while trying to stop a major crime. This action, which goes against his no - killing rule, makes the public and the law turn against him, sending him to jail. In jail, he has to face his own inner demons and also deal with the threats from other inmates who see him as a big target.
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.
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.
There could be a new character, a jailmate of Percy. This character could be either a friend who helps Percy survive in jail or an antagonist who makes his life more difficult. For example, a tough guy who wants to bully Percy at first but later has a change of heart.
In a 'Harry Potter goes to jail' fanfiction, perhaps Harry breaks a new law that the Ministry of Magic has created to maintain control. For example, if he tries to teach magic to non - magic people in an attempt to prepare them for a potential dark wizard threat. The Ministry, fearing chaos, throws him in jail. Inside, he meets other wrongly - imprisoned wizards and they plan an escape together while also fighting against the unjust system.
Maybe he was framed by a powerful villain. The villain planted evidence to make it seem like Spider Man committed a serious crime, and without a chance to fully prove his innocence right away, he was sent to jail.
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.
Maybe it's about Harry being wrongly accused and his fight to prove his innocence while in jail. He could be making friends with some unlikely characters in the jail who help him in his quest.