Deku's Quirk From My Hero Academia Explained
As the protagonist of the anime "My Hero Academia," you might be surprised to learn that Izuku "Deku" Midoriya was born with no super powers (AKA Quirks). After all, how is a quirkless person supposed to become a hero in a world where 80% of the population has some kind of quirk? Before you think "My Hero Academia" is a show about a boy learning to Batman his way to being a hero without powers, we encourage you to learn a little more about Deku and his journey towards becoming the #1 hero of his time.
At the beginning of "My Hero Academia," the quirkless 14-year-old Deku has absolutely no chance of making it as a hero. However, a few chance encounters with his idol, the #1 hero All Might, change that. Deku's passion for all things hero-related and strong heroic instinct motivate the All Might to reveal one important secret to Deku: He can become a hero by taking on All Might's quirk.
As it turns out, All Might's quirk — which is a mystery among his fans — actually has a few abilities. Firstly, it makes him unfathomably fast and strong. Secondly, and more importantly, it can be transferred to others. It is called "One For All" and has been passed down for generations. However, that's only the tip of One For All's iceberg. There's a lot more regarding Deku's quirk that has left to be explained.
One For All is pure power
In order to understand One For All, it's important to know the basics. Aside from its ability to be transferred between new users as All Might does to Deku, One For All is simply a crystallization of power. From the time of its original user, the Quirk's only purpose has been to store pure power and pass it onto the next generation. As such, a One For All user has access to more strength, speed, and stamina than the average person can imagine. In addition, any user's pre-existing quirk is enhanced by One For All's effects. Over the decades, the quirk has amassed so much power that a relatively "light" punch carries enough force to change the surrounding air pressure and cause rainstorms (though this rarely happens).
To utilize that amount of force, Deku had to undergo an excruciatingly difficult workout regime, clearing large debris from a local beach and pushing his body to its limit for ten months before All Might passed the quirk down to him. After those ten months, Deku's body was still only capable of acting as a vessel. If he tried to use One For All, the immense power of the quirk would severely injure him. It wasn't until Deku underwent further training that he was able to use some of One For All's power without crippling himself. Even then, he had to use it differently from his predecessor, focusing more on speed than power.
That power only grows as it lives on
One For All wasn't always so ridiculously powerful, however. Its intended purpose is to accumulate power over time. How exactly it stores this power is a mystery. How it transfers it, however, is not. To pass on One For All, the quirk's current user must give a sample of their DNA to be imbibed by their successor. In Deku's case, All Might gave him a hair to eat. On top of that, the One For All user must desire for their quirk to be passed on to that person. As such, it is impossible to steal One For All.
The downside to this system is that One For All can be coerced or forced onto a person through outside means. Drinking All Might's Blood like a deranged vampire won't give you One For All, but forcing an ultimatum on him that requires him to pass it on (even though he might not want to) could. For this reason, One For All users keep the nature of the quirk a closely guarded secret. Aside from Deku, only All Might's closest allies know exactly how it functions. Even fewer know of all the other One For All users.
Where did One For All come from?
In total, All Might is the eighth in a long line of One For All Users. However, One For All's origins are much more unique than you might think, even considering the prestige of its users. Generations prior to the events of "My Hero Academia," a villain known as "All For One" stood as the world's greatest threat to peace. With the power to absorb other people's quirks, combine them, and pass them to others as he saw fit, he amassed many followers.
His younger, quirkless brother had a strong sense of justice. In a bid to control his sibling, All For One gave him a quirk that could store power. However, the young man thought to be quirkless actually did have a quirk, one that combined with the power imparted by All For One. His otherwise useless quirk simply had the ability to be passed on, and the resulting quirk combo created One For All. Unfortunately, the man was too weak to face his sibling, and so passed his new quirk to others.
There is another unintended side effect to this process. Fragments of each user's consciousness exist within One For All as a whole, and reside in some form within each new user. Because of this, their quirks also remain. Under the right conditions, a user might even be able to take on the other quirks of their predecessors, something which only Deku accomplishes.