The latest chapters of My Hero Academia's War Arc have been delving deeper into what the series' central warring powers - One For All and All For One - are truly all about. The two current avatars of the powers - Izuku Midoriya and Tomura Shigaraki (respectively) - have both lost themselves to the grip of the living entities inside both OFA and AFO. As the fight has moved to a mental/spiritual plane of battle, My Hero Academia has once again confirmed a key detail of the One For All power - and how it can, or cannot be, passed on to others!
Warning: My Hero Academia Chapter Manga SPOILERS Follow!
In My Hero Academia chapter 287, Izuku is and Shigaraki face-off in the realm of OFA. Deku is backed by the power of OFA user Nana Shimura and the power's original user; Shigaraki finds himself possessed by the consciousness of All For One the man. The purpose of the face-off is simple: All For One has invaded One For All's realm in order to steal the power once and for all. However, despite an earnest effort on the villain's part, he cannot take One For All away from Deku.
The key reveal in this chapter comes from All For One, who explains that quirks aren't just superpowers - they contain part of the spirit of its wielder:
"Just as organs and cells house memories of sorts," All For One explains. "Every quirk factor contains a consciousness - the individuality of its wielder if you will."
In the case of OFA, the combined living consciousnesses of its users prevent the power from just being taken by All For One, like so many other quirks the villain has stolen. One For All has to truly be bestowed upon a person. However, like any rule there is one caveat: the force of Tomura Shigaraki's will and rage is enough to overpower the laws of OFA and affect its realm.
Ultimately, the power of One for All's users is enough to expel Shigaraki from and All For One from the OFA realm. In the aftermath, OFA seems to make a more complete attachment to Deku, as the will of its users decides that Izuku is the most selfless hero they've ever seen.
We know have further confirmation that OFA is indeed a living power, which is able to carry consciousness forward through generations. What these developments are building to is anyone's guess; there are still the mysteries of OFA's 4th user; how the power will evolve now that it is fully in sync within Izuku; and what can happen if Tomura Shigaraki's emotional intensity and power is full applied to siphoning the power. That's enough intrigue to propel My Hero Academia well beyond this war.