My Hero Academia is a popular shounen anime and manga series.
It is set in a fictional world where 80% of the population possesses some kind of uncanny ability, called quirks.
The story centers around a 15-year-old high school student, Izuku Midoriya who aims to become the world's number one hero.
The manga recently concluded the Paranormal Liberation War Arc and the consequences were dire.
The world of the heroes is taking a turn in another direction. Unfortunately, the change doesn't seem to be a good one right now.

The source behind this chaos and worldwide panic is one man named All For One.
He is the central antagonist of the series and the arch-nemesis of all One For All wielders.
This frightening man has an unknown number of powerful quirks at his disposal.
To make things worse, he has been around for more than a century.
Even in a superhuman society, immortality is not something that people come across often.
The secret behind his immorality remains one of the greatest suspense of the series.
Here, we will unveil the truth behind All For One's immortality. This article has a lot of spoilers from the manga.
Early Life of All For One

The arrival of supernatural abilities in a mundane world led to a period of societal collapse and age of upheaval.
A few people started being born with varying physical appearances, causing them to be shunned by "normal" people.
This led the victims of ostracization to use their ability for the sake of revenge and evil.
The man who stood at the pinnacle of all that chaos was All For One, whose real name remains a mystery to this day.
He gathered those people, brainwashed them, and used them to their own advantage.
He took the power of those who didn't need it and gave it to those who didn't have any.

This way, he created an army for himself and set the world on a path of destruction.
He never showed himself to the public, always ruling behind the shadows.
Up till the third season, the world believed All For One to be some kind of myth or Urban Legend.
The Truth Behind All For One's Immortality
All For One claimed to love his younger brother (Yoichi Shigaraki), who had a feeble body and no quirk.
He used all kinds of ways to persuade his younger brother to choose a quirk of his liking and joining his mission.

However, Yoichi never once believed him and refused to help in any way.
Unfortunately, All For One forced forcefully gave Yoichi a quirk that could stockpile power in order to make use of him later.
It was during this time when All For One first met Kyudai Garaki.
Kyudai theorized the "Quirk Singularity" and claimed that there will come a day when Quirks will become so powerful that no one will be able to control them.
Society scoffed at his claims and Kyudai completely disappeared from the public's eye.

Unfortunately, All For One believed his claim and blended him his aid.
Since then, All For One and Kyudai Garaki have worked towards a single goal.
Kyudai Garaki later adopted the name Daruma Ujiko and is responsible for many heinous acts.
This includes healing All For One after his first fight with All Might and boosting the powers of Tomura Shigaraki before the Paranormal Liberation War Arc.
He also created all the Nomus in the series.

Kyudai had a quirk called Life Force which doubles the life span of the user.
Kyudai gave his original quirk to All For One voluntarily and kept the duplicate copy for himself.
This is how they both have survived for over a hundred years.
So, unlike how it was hinted in the series that All For One is immortal, the truth is that he merely has double the lifespan of an average human.
How Does Lifeforce Work?
Lifeforce simply allows the user to double their life span, causing their aging process to decrease by half.
This makes the user look much younger than they are.
As of the present, All For One is over a hundred years old and Daruma Ujiko is over 120 years old. H
owever, they both look like middle-aged men.
This quirk drastically decreases the physical mobility of the user.
This is why Daruma was especially weak in person and never engaged in battle despite being a villain.
However, somehow All For One managed to overcome the weakness provided by this quirk.

Having multiple strong quirks may be the reason behind this.
Another weakness of this quirk is that it can easily lose its effect once it is canceled out.
In the Paranormal Liberation Arc, when the heroes cornered Daruma in his base, Erasure Head used his quirk on him, which caused the former to drastically become old and extremely weak.
Daruma was soon imprisoned after that.
