Perhaps it's an ancient demigod who was too powerful for the gods' comfort. They locked him away to prevent him from overthrowing their rule. This demigod could have unique abilities that are now lost to the modern demigods, and Percy's encounter with him could bring back those powers or knowledge.
It could be an old Titan who was locked away by the Olympians. Maybe one who was not as evil - minded as the others and was wrongly imprisoned.
It might be a primordial being that was sealed away long ago. For example, a being from the chaos before the gods were born. The gods imprisoned it to maintain order in the world, but now, with new threats emerging, Percy might find that the being could be an ally or a powerful weapon if he can control it.
Perhaps the ancient prisoner is actually a wronged hero from the past. Percy discovers this and has to fight against the forces that want to keep the prisoner locked up, all while dealing with the internal politics of the demigod world. The prisoner could hold the key to a new kind of magic or weapon that the demigods need to defeat an upcoming evil. It could also be that the prisoner has a connection to Percy's family history, and by freeing him, Percy learns more about his own heritage and powers.
Many ancient novels had plots about prisoners traveling to ancient times, such as Jia Lian in Dream of the Red Chamber, Lin Chong in Water Margins, and so on. The protagonists of these novels were usually transported to ancient times and became prisoners of some aristocrat or bureaucrat, but through their own efforts and wisdom, they gradually escaped from the predicament and became useful characters. These novels often involved love, friendship, loyalty, betrayal, and so on. The ups and downs of the plot were memorable.
😋I recommend the following two novels to you: The Evil King's Favorite Wife: The Prisoner's Concubine Steals the King's Heart and The Tyrant's Favorite Prisoner's Concubine: Your Highness, Greetings. The former was about the day of the female protagonist's wedding. Her husband was the enemy of the country, and the female protagonist was willing to be his imprisoned concubine. The latter was about the story of the return of the missing young lady. She no longer had the heart to kill them, but instead, she had more schemes and a nightmare that she could not escape from. I hope you like this fairy's recommendation. Muah ~😗
Maleficent could be a great villain in this fanfiction. Her connection to dark magic makes her a natural fit for the setting of the prison of darkness. She could be the one who put Kairi there or be trying to manipulate her for her own evil plans.
It could be a rogue ninja from the Sand Village who has a grudge against the 'Prisoner of Sand'. Maybe this rogue ninja was once betrayed by the 'Prisoner of Sand' or their family and now wants revenge.
One possible plot could be that Prisoner 777 is part of a larger conspiracy. He kidnaps Anzu as part of a plan to disrupt something in the world of the fanfiction. For example, if Anzu has some special power or knowledge, he might want to use her or stop her from using it. He could be working for an evil organization that wants to gain control over a certain aspect of the fanfiction world.
One possible plot could be that Hermione was wrongly accused of a serious crime against the wizarding world. Maybe she was framed by a dark wizard who wanted to silence her for her intelligence and knowledge. She might be struggling to prove her innocence from within Azkaban while her friends on the outside, like Harry and Ron, are desperately trying to find evidence to free her.
I don't know which novel 'The Green Prison' is referring to. As someone who loves reading novels, my knowledge comes from a large amount of text data, including web articles, novels, news, encyclopedia, and so on. I can answer questions on a wide range of topics, but I can't.
I don't know who the author of 'the prisoner a novel' is. There are so many novels out there and without more context, it's difficult to determine.
I recommend an ancient romance novel called "The Fickle Queen." Although the name doesn't have the word "prisoner" in it, the protagonist is charged with escaping from marriage and has to be executed. She did not want to run away from the wedding. She only had the beautiful dream of becoming a princess consort or an empress in her heart. This novel was full of the female protagonist's determination and hard work, and at the same time, there was also the appearance of the handsome prince. I hope you like this fairy's recommendation. Muah ~😗