Well, a common storyline in My Hero Academia demon quirk fanfiction is the origin story of the quirk. It could be that the character got the demon quirk from a mysterious experiment gone wrong. Then there's the idea of a character with a demon quirk having to hide it from society because it's seen as too dangerous. And of course, there are those stories where the character with the demon quirk has to fight against other demons or dark forces that are attracted to their power.
One cool quirk idea could be 'Shadow Mimicry'. The user can blend into any shadow and move freely within the shadow realm, also being able to mimic the actions of those whose shadows they are in. It gives a lot of stealth and surprise attack possibilities in a fanfiction.
Authors can start by giving the character a unique appearance. For a demon quirk, it could be horns or red eyes. Then, they should give the character a complex personality. Maybe the character is shy because they're afraid of being judged for their quirk. Also, give the character some flaws related to the quirk, like it drains their energy too quickly.
One popular storyline could be about a character receiving a mysterious gift that unlocks a new quirk or power. For example, Midoriya might get a gift from an unknown source that gives him the ability to control time for a short period, adding a whole new dynamic to his battles and character development.
One popular storyline is the 'What if' scenarios. For example, what if the main character had a different quirk? Another is the character development outside the canon story, like exploring Bakugo's past more deeply. And there are also storylines where minor characters get more spotlight and their own heroic arcs.
The 'Underdog to Hero' trope is also common. Even when Izuku has a new quirk, he often starts off being underestimated. He has to prove himself not only to his classmates but also to the heroes around him. This trope is great for character development as we see Izuku grow in confidence and skill.
His quirk could be something like 'Limitless Rage - Transformation'. When he gets angry, his body transforms into the Hulk form, growing in size and strength. The angrier he gets, the more powerful he becomes, similar to how it works in the Hulk's original story.
The 'Plant Symbiosis' quirk would be a great addition to a fanfiction. The individual with this quirk can form a symbiotic relationship with plants. They can communicate with plants, make them grow rapidly, and even use plants as an extension of their body for things like creating shields or lashing out at enemies. This quirk could bring a whole new element of nature to the story.
One popular storyline is about two female hero students falling in love while training together. They support each other in their growth as heroes and their relationship develops over time. Another common one is a story where a female villain and a female hero have a complex relationship that turns into a romantic one.
A common storyline is about a female sidekick who eventually steps into the spotlight. She's been in the shadow of a more well - known hero for a long time. But due to a particular incident, she has to take charge and prove herself. This shows the growth and empowerment of female characters in My Hero Academia fanfiction.
One popular storyline could be Ryuko's training journey. Maybe she discovers a new quirk ability during intense training sessions and has to learn to control it. This could involve her seeking advice from her teachers or more experienced heroes.