One idea could be exploring the backstory of the main character in the 'dark paradise'. Maybe they had a difficult childhood that led them to the dark situation they are in now.
You could also focus on a love story within the 'dark paradise'. Two characters who are from different sides or have different goals fall in love, and their relationship changes the dynamics of the whole place.
A plot could involve a character from 'Dark Paradise' falling in love with a character from 'Twilight'. But there are many obstacles like the different natures of their worlds and the existing relationships in 'Twilight'. For example, if a Dark Paradise character, who might have a different concept of love and loyalty, tries to court a Twilight character who is already in a complex relationship. This could create a lot of drama and conflict.
One idea could be Percy exploring a hidden part of the paradise that has magical creatures never seen before. He could form an alliance with them to protect the paradise from an outside threat.
Well, you could write a fanfic where a new type of kaiju is introduced into Kaiju Paradise. This kaiju has unique abilities that no one has seen before. The main character is a scientist or a researcher in the park who tries to study this new kaiju. Along the way, they face challenges from the park's management who don't want the public to know about this new discovery, and also from the kaiju itself which is very unpredictable.
One idea could be a new student arriving at Paradise High with a special ability that both helps and complicates the assassination attempts on Koro - sensei. For example, they might be able to sense his weak points more acutely but also have a personal vendetta against the students trying to kill him.
In a 'dark blood Naruto fanfic', the dark blood could give the wielder the ability to see the darkest secrets of others. Naruto, with his new power, uncovers a conspiracy within the ninja world that is far more dangerous than anyone thought. He has to use this power, which is feared by many, to save the world while also dealing with those who want to stop him because of his 'dark' ability.
Another plot idea might be an OC who is on a quest to find a long - lost relative who was taken by the Crimson King. This OC could team up with the main characters like Roland. Along the way, they face challenges like dealing with the various creatures in the wastelands and trying to decipher the riddles left by the Man in Black.
A great plot could involve a character who has a unique ability to resist the sanity - draining effects of the game's environment and uses it to help others. They could be on a mission to find a way to end the horror once and for all. For example, they might discover a hidden chamber with a powerful artifact that can reverse the curse of the castle.
One idea could be a crossover where the Jedi from Star Wars encounter the moral dilemmas similar to those in The Dark Knight. For example, a Jedi might face the choice of using a dark side power to save many, like Batman's tough decisions. Another could be a Sith lord with the Joker's chaotic nature, causing havoc in the Star Wars universe. Maybe a young padawan is influenced by this Sith - Joker figure and has to struggle between the light and dark within himself, just as characters in The Dark Knight trilogy often struggle with their own morality.
Perhaps an OC who was turned dark due to a curse. They could start off as a normal demigod but after being cursed by a powerful enemy, they gradually become more malevolent. Their journey could involve trying to break the curse while also being hunted by other good - minded demigods.
Maybe Ahsoka gets captured by a dark side cult. They try to convert her by showing her their version of 'justice' through the dark side. They expose her to their cruel and efficient ways of dealing with enemies, which makes her question her Jedi teachings. However, she eventually realizes that their 'justice' is just tyranny in disguise.