It could be that a certain event or discovery changes the perspective of the characters. For instance, a ghoul might find out that there are some humans who are willing to accept them. This new - found acceptance could be the light in their dark existence as outcasts in the society of Tokyo Ghoul. It would then lead to a series of events where the character tries to bridge the gap between the two species.
Maybe it's centered around a group of characters, both human and ghoul, who come together to fight against a greater evil in the Tokyo Ghoul world. Their unity and determination could be the 'light'. Well, in this fanfiction, they might face many difficulties as humans and ghouls have different natures. But through mutual understanding and cooperation, they strive to make the world a better place.
It could be about exploring the themes of hope or moral struggle within the dark and complex world of Tokyo Ghoul. Maybe it focuses on a character who is like a 'light' in the midst of all the chaos and horror that the Tokyo Ghoul universe presents.
The plot could involve a shared threat that forces the Tokyo Ghoul and Parasyte universes to collide. Maybe a new type of organism emerges that is even more dangerous than ghouls or parasites. The characters would then have to combine their unique abilities to combat this threat. For instance, Kaneki's kagune and Shinichi's enhanced physical abilities with his parasite Migi could be used in tandem. This would create an interesting dynamic as they try to figure out how to work together while also dealing with their own internal struggles related to their inhuman natures.
One possible plot could be that the oc is reborn as a ghoul in the Tokyo Ghoul world. They struggle to come to terms with their new identity and the need to feed on human flesh. They could try to find a way to co - exist with humans without causing harm, perhaps by joining Anteiku and learning from Kaneki and the others.
One possible plot could be that Uta, with his unique mask - making skills from Tokyo Ghoul, gets involved in a situation where he has to create a special mask for a character from the Uta no Prince - sama world. Maybe this mask gives the Uta no Prince - sama character some special powers related to the ghoul world, like enhanced hearing or the ability to see in the dark. And then they have to navigate through both the music - filled world of Uta no Prince - sama and the dangerous world of Tokyo Ghoul together.
One possible plot could be that Naruto and his friends are sent to the Tokyo Ghoul universe by some sort of space - time jutsu gone wrong. Naruto, with his strong sense of justice, would be immediately intrigued by the situation of the ghouls. He might try to find a way to co - exist between humans and ghouls, using his ninja way. He could team up with some of the more sympathetic ghouls, like Kaneki, and together they fight against the more extreme elements on both sides, whether it's the violent ghouls who only see humans as food or the humans who want to exterminate all ghouls without question.
A plot might involve a ghoul ending up in the Loud House world. This ghoul could be on the run from other ghouls or the CCG in its own world. In the Loud House, it has to hide its true nature from the Loud family while also trying to adapt. The Loud kids start to notice strange things happening around the house, like missing food (because the ghoul needs to eat). Eventually, they discover the truth and have to decide whether to help the ghoul or turn it in.
A plot might involve a magical accident that transports some of the Tokyo Ghoul characters into the wizarding world. Kaneki could end up at Hogwarts and be sorted into a house. He'd struggle to hide his ghoul identity while also trying to find a way back home. At the same time, the wizards are intrigued by his unique abilities and some, like the more power - hungry ones, might try to use him for their own gain. Harry Potter and his friends would then have to decide whether to trust Kaneki or not.
The theme of survival is also prominent. Ghouls need to hunt and feed on humans to survive, while humans are trying to defend themselves from ghouls. It creates a complex web of predator - prey relationships. Also, there is a theme of identity. Kaneki's transformation into a half - ghoul makes him question who he really is, is he a human, a ghoul, or something in between?
One of the main themes is the struggle between different species. In 'Tokyo Ghoul', there's a constant battle between humans and ghouls. Another theme is identity. The main character, Kaneki, has to deal with his new identity as a half - ghoul and how that changes his view of himself and the world around him.
One plot idea could be your OC being a new ghoul trying to find their place in the ghoul society. They might start at the bottom, having to learn the rules of the different ghoul groups and facing discrimination from more established ghouls. Another idea is that your OC discovers a secret about their transformation that no one else knows, like it was part of a secret experiment by the CCG. They then have to figure out what to do with this knowledge while also avoiding being caught by the CCG.