My Hero Academia Season 6, Episode 18 – “Izuku Midoriya and Tomura Shigaraki,” marks the beginning of the first arc of the final act saga. Hero society has suffered from the events that occurred after the Paranormal Liberation War. Most of the top villains are free from prison and causing chaos in Japan. The civilians of Japan have lost confidence in the heroes. Deku is hospitalized after his fight with Tomura. He enters the Vestige World where most of the previous One For All users are present.
The first user, Yoichi Shigaraki, tells Deku that they now have the ability to interact with him directly. Deku isn’t completely able to manifest himself but his mouth is still gone, however, his voice now works. Hikage Shinomori, the fourth user, died of old age at the age of 40. It turns out that One For All drains the life force out of the user. This particular problem is the result of the user possessing multiple Quirks.
Deku leaves U.A.
Deku realizes that All Might was able to use One For All so effectively and long because he was like Deku, Quirkless. In the My Hero Academia universe over 80 % of people have Quirks. Genetically speaking the Quirklessness gene is recessive, when Quirkless people are given Quirks it can do a great deal of damage to the body. For example, Yuga Aoyama was given the Navel Laser by All For One. His body can’t handle it, so the Navel Laser “leaks,” out and can cause him to “lose control of his bowels.”
As time goes forward the likelihood that Quirkless people will be born will decline further potentially meaning that the One For All Quirk will die off. However, because All Might survived he was able to pass on knowledge to the vestiges. Hikage believes that only a vessel without a Quirk can wield One For All. Elsewhere, the other heroes recover from their injures during the war, while Hawks, Best Jeanist, and Endeavor face the public. Hawks and Endeavor confirm the truth of their personal lives. Later, Deku decides that the best way for him to protect everyone is to leave U.A.