Another aspect of Daki fan fiction could be the alternate universes. What if Daki was never a demon? How would her life be? These are the kinds of creative ideas that can be explored in fan fictions, and they often attract fans who want to see different interpretations of the character.
One popular theme is redemption. Since Daki is a demon, some fan fictions might explore the idea of her finding a way to redeem herself. This could involve her making amends for the harm she has caused to humans.
Nezuko is initially 12 years old in the manga. As the story unfolds, her age doesn't change significantly in a traditional sense, but her character development is quite remarkable.
The Harry Potter fandom is great for oc fanfiction. There are so many aspects of the wizarding world to explore, like creating a new student at Hogwarts with unique magical abilities. Another good one is the Star Wars fandom. You can create original characters within the vast galaxy, perhaps a new Jedi or a smuggler in a far - off system. The Marvel Cinematic Universe is also a top choice. You could develop an original superhero or villain with powers related to the existing lore.