One idea could be Izuku struggling to control his shadow quirk at first. Maybe it has a mind of its own and he has to learn to cooperate with it. For example, in battles, the shadow could act independently, which might cause trouble but also surprise opponents. Another plot could involve Izuku using his shadow quirk to explore hidden or dark places. Since shadows can reach areas that are hard to access, he could use it for rescue missions or to find secrets in the city.
Well, a plot idea could be that Izuku discovers his shadow quirk has the ability to merge with other shadows. He starts off by accidentally merging with his friends' shadows, which causes some comical and confusing situations. But as he gets better at it, he uses this ability to gain strategic advantages in battles. He can hide in the merged shadows, or use the combined strength of multiple shadows to overpower his enemies.
One idea could be that Izuku's quirk is related to time manipulation. He could use it to slow down time during battles, giving him an edge in combat. For example, he could dodge attacks with ease and plan his counter - attacks carefully.
One idea could be a villain who can steal quirks and is secretly a former hero trainee who was wronged. They start stealing quirks to create a super - powerful army to take revenge on the hero society that failed them.
Perhaps a story where a Copy Quirk hero is framed for using villainous quirks they copied in self - defense. They then have to go on the run and prove their innocence. Along the way, they meet other outcasts and form an unlikely team. They use their copied quirks in creative ways to avoid capture and expose the real villain who set them up.
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.
One plot idea could be that Izuku and Momo are paired up for a special training mission. They have to learn to combine their quirks in new and unexpected ways. For example, Izuku's super strength could be used to enhance Momo's creation of large and complex structures. Another idea is a story where they both get trapped in an alternate dimension and have to rely on each other to find a way back. They face various challenges that test not only their quirks but also their friendship and trust in each other.
One idea could be that Toga, in an attempt to understand Izuku better, tries to live a normal life like him for a while. She disguises herself and enrolls in U.A. High, leading to a series of comical and tense situations as she tries to hide her true identity from Izuku and the other students.
One idea could be that Shoto and Izuku have to team up for a special training exercise that goes horribly wrong. They end up in an unknown part of the forest and have to rely on each other's quirks to survive and find their way back. For example, Izuku uses his One For All to climb tall trees to get a better view, while Shoto uses his ice to create shelters at night.
One possible plot idea could be Izuku developing a new and unique quirk spiral ability that sets him apart from his peers. Maybe it starts as an unexpected mutation of his existing power. Another idea could be Izuku getting caught in a time - spiral within the My Hero Academia universe, where he has to relive certain events to change the outcome for the better. And a third could be Izuku's spiral being related to a spiritual or mental journey, where he discovers hidden aspects of himself and the hero world.
There are also fanfictions where Izuku's quirk has a hidden aspect. Maybe his connection to One For All unlocks memories or abilities from the previous users in a more profound way. For instance, he might be able to access the combat knowledge of the past users directly, almost like having an in - built combat instructor guiding his every move.
One idea could be fusing Bakugo's explosion quirk with Todoroki's ice quirk. Imagine a hero who can create explosive ice shards. It would be a visually stunning and powerful ability. Another could be fusing Uraraka's zero - gravity quirk with Midoriya's One For All. The hero might be able to make objects weightless and then send them flying with super strength.