Perhaps a plot where the magic that exists in the Clannad world is more fully understood and harnessed by the characters. This could lead to new ways of solving the problems they face, such as Nagisa's health issues. Also, a story about the characters in a post - Clannad world, how they are building their new lives and families.
A really interesting plot could be about time - travel within the Clannad universe. Tomoya could go back in time to try and prevent some of the sad events that happened. This would involve him interacting with his past self and trying to change the course of events without disrupting the overall fabric of the Clannad story.
One idea could be a crossover with a magical girl anime like Sailor Moon. Clannad characters could find themselves in a world where they have to fight alongside the Sailor Scouts against a common enemy. Maybe Nagisa discovers she has latent magical powers and has to learn to control them with the help of Usagi.
In Clannad fanfiction, a common concept is the expansion of relationships. There might be fanfictions that develop the friendship between Nagisa and Kyou in more detail. Or perhaps show how the relationship between Tomoya and his father could have been mended in a different way. Some might also explore the idea of characters having superpowers or special abilities in a Clannad - like setting, which would be a really unique take on the original story.
One idea could be a what - if scenario where Naruto becomes a rogue ninja. This would completely change the dynamics of the story and his relationships. For example, he might be hunted by his former friends, and we could explore his inner struggle and reasons for turning rogue.
A really interesting fanfiction plot could be about a group of scientists who were working on a project to reverse - engineer the demon technology. They think they can use it to create a weapon against the demons. However, things go wrong and they accidentally open a new portal to a different demon dimension, which brings in even more powerful and unknown demons. The story could then focus on how they deal with this new threat and try to close the portal.
One idea could be a story about an ordinary villager in Maple World who discovers a hidden power within themselves. Maybe they find an ancient artifact that gives them the ability to communicate with monsters and they use this power to broker peace between the villagers and the monster tribes.
One idea could be that Cinderella is a secret superhero. By day she endures the cruelty of her stepfamily, but by night she uses her superpowers to help the poor in the kingdom. Another could be that the prince is actually under a curse too, and only Cinderella's true love can break both their curses. Or perhaps Cinderella is an inventor in disguise, creating amazing gadgets that she uses to outwit her stepfamily.
One idea could be a story where a young trainer discovers a rare and powerful Pokemon that has the ability to communicate telepathically. This Pokemon could lead the trainer on a quest to find a hidden place full of ancient Pokemon knowledge.
In a modern - day cinderella story fanfiction, Cinderella could be a struggling artist. The prince is a wealthy art collector. They meet at an art exhibition instead of a ball. Cinderella's art catches the prince's eye, and he is determined to find the artist behind it, leading to their love story.
One idea is that Greninja is framed for a crime it didn't commit. It then has to go on the run while trying to prove its innocence. Along the way, it teams up with other outcast Pokémon and together they uncover a conspiracy that goes far deeper than they ever expected.
One idea could be exploring the Marauders' time at Hogwarts in more detail. For example, showing how they formed their friendship and the pranks they played on Snape that weren't in the original books. Another plot could be a time - travel fanfiction where a character from the future goes back to the Marauders' era and tries to change certain events. Or perhaps a fanfiction where the Marauders have to deal with a new dark threat at Hogwarts that no one else is aware of.