One idea could be exploring the backstories of the minor characters in Deadman Wonderland. For example, you could write about how a particular inmate ended up in the prison. Another could be a what - if scenario, like what if Ganta had different powers. Maybe he could control water instead of his blood bullets.
You could write a fanfiction where the inmates of Deadman Wonderland manage to overthrow the corrupt system. This would involve a lot of planning, character development as they form alliances, and intense action scenes. The story could focus on how they deal with the power vacuum left after overthrowing the existing regime and how they try to create a new, fairer system within the prison walls.
One idea could be a crossover where Naruto characters are trapped in Deadman Wonderland. For example, Naruto could use his shadow clones to deal with the various challenges and enemies in the prison. Another idea is to explore how the powers in Deadman Wonderland would be used by Naruto characters. Maybe Sasuke could master some of the blood powers in a unique way. And a third idea could be a story where the main Naruto characters have to form alliances with the Deadman Wonderland inmates to escape the prison together.
One idea could be a crossover with 'Attack on Titan'. The Deadman Wonderland characters could find themselves in the world of Titans and have to use their unique abilities to survive. For example, Ganta's ability to shoot his blood bullets might be useful against the Titans. Another idea is a crossover with 'Fullmetal Alchemist'. The alchemical world could interact with the prison - like setting of Deadman Wonderland, and perhaps there could be a search for a way to break the curse in Deadman Wonderland using alchemy.
A plot could involve Shiro getting sick. In Deadman Wonderland, there are no proper medical facilities for inmates. Ganta has to find a way to cure her. He teams up with some of the other more friendly inmates to search for a cure. This story could show how far Ganta is willing to go for Shiro and also how the other inmates view their relationship.
One idea could be Harry finding himself in Wonderland during a strange magical accident at Hogwarts. He could encounter the Cheshire Cat as a magical creature that can disappear and reappear, leading him on a quest to find a way back home while also uncovering secrets about the Wonderland's connection to the wizarding world.
One idea could be that Alice returns to Wonderland as an adult and finds it has changed completely. The once friendly characters are now in a state of chaos due to a new dark force. Another could be a story where Wonderland is connected to our world in a more secretive way, and Alice has to keep the balance between the two. Or perhaps a fanfiction where Alice teams up with the Cheshire Cat to solve a mystery that involves all the Wonderland characters and their forgotten pasts.
One idea could be Harry finding a hidden portal in Hogwarts that leads him to Wonderland. There, he meets the Cheshire Cat who helps him understand some of the mysteries of the wizarding world in a different way. Maybe he has to solve Wonderland - like riddles to get back to Hogwarts.
One idea could be the Digimon characters getting lost in Wonderland. They might encounter the strange creatures of Wonderland and have to figure out how to get back to their own world. For example, Agumon could meet the Cheshire Cat and have a confusing conversation about directions.
Well, perhaps in the fanfiction, the Queen of Hearts is allergic to lemons. And Alice, unknowingly, brings lemons into the Queen's court. This causes chaos as the Queen starts sneezing and her usual angry outbursts are now mixed with her allergy-induced irritation. It could lead to a series of comical and adventurous events as Alice tries to fix the situation.
One interesting plot could be a time - travel story in the Harry Potter wonderland. For example, a character goes back in time to the Marauders' era and gets involved in their adventures, while also trying to prevent a future disaster in the wizarding world. Another idea is a story where a new, powerful magic is discovered in the wonderland, and Harry and his friends have to figure out how to control it before it falls into the wrong hands. A third plot could be about an alternate reality where Voldemort won the war, and the remaining good characters have to find a way to reverse the situation in the harry potter wonderland.
A really interesting plot would be if the characters from Alice in Wonderland were students at Hogwarts. Alice could be in Gryffindor, always getting into strange adventures around the school that remind her of Wonderland. The Mad Hatter could be a Potions master who makes the most bizarre potions. And the Red Queen could be a strict teacher who is always trying to catch students breaking the rules. There could also be a plot where Voldemort tries to take over Wonderland for some dark purpose, and Harry and his friends have to stop him there.