Currently writing a fanfiction called Challenger, a spinoff of Uru-chan's unOrdinary. A sort of a fan parallel dimension, if you will.
Grey (inspired off of John Doe) is a 17-year-old highschool student-soon-to-be-hero, but, like all his other classmates, he has an Ability. 95% of humanity have been born with a single Ability, but the powerless 5% lucked out and ended up as a cripple.
Let me explain how Abilities work: Abilities are powers that people are born with, though the manifestation time differs per person; few individuals displayed their Ability at birth, but most discover their Ability when they are 5 or 6 years old. Hereditary Abilities are passed from the parent/s to the offspring, though parents without abilities can have a child with abilities, and children can sometimes possess Abilities that are different from their parents Abilities. Whenever an Ability is used, it usually gives off an Aura in the user's hair or eye color. It flows through Aura Channels which regulate he flow of Aura through the body. A stronger flow of Aura naturally results in a stronger Ability. Normally, the aura flow cannot be altered by consciously, though Meta Abilities (Aura Gage and Aura Manipulation) allow the user direct control to their Aura Channels.
Abilities usually have some kind of drawback, and the more powerful the Ability, the stronger the drawback. For example, the Ability Shield allows the user to create shields that reflect damage and are almost impenetrable; should they break, however, it can cause physical damage to the user. The Ability Hellfire, if used to long or too much, will begin to consume the user. Any kind of ability that transforms the user (e.g., Stone Skin, Invisibility, etc.) drains their stamina when powered off and can eventually cause pain throughout that body and possible damage.
A boy with a troubled past, Grey is naturally a good kid, but has a tendency to violence, and swears to destroy the system of hierarchy that places the strongest at the top of the social food chain, leaving the weak helpless and at the mercy of the higher tiers. He charades as a cripple (though his closest group of friends know about his power, and try to help him with his past), but is actually one of the strongest in his school. His Ability, Aura Manipulation, allows him to detect, manipulate and copy Auras, allowing him to observe the Aura Flow in other power users, copy their Abilities, and combine them in order to produce devastating results (e.g., copying and combining Fire and Wind produces Firenado, not a separate Ability but a combination of the two; some Abilities failed to combine, so not all abilities are compatible). The only limitations so far is that he can copy up to 4 abilities, and he can only use them for a short time period.
Grey has successfully dethroned the Houses (group of "elite" students at a school) of both New Bostin, Southport and Wellington High, and there is seemingly no end to his power. What are some possible nerfs that can be implemented to his power?
(P.S.: Abilities are pseudoscientific, not magically or otherwise.)