It’s a secret that’s been swept under the rug for the entirety of the series. Does Deku tell everyone about One For All?
Yes, Deku does tell everyone about One For All. He admits the truth about his power in a series of letters he left behind for his classmates. The letters explain that his power came from All Might, and he must leave the school as Shigaraki and All For One look to steal his quirk.
Deku leaves the Hero Academy for the safety of himself and those around him.
Deku decides tells everyone about One For All
In chapter #306, Endeavor is conducting a press conference in response to allegations put forth by his son, Dabi. During the conference, reporters ask about the One For All power, but denies any knowledge on the subject.
The chapter wraps up with a scene from the U.A. dorms. A narrator explains that Endeavor pretends not to know the identity of One For All so that Deku and All Might would not have targets on their backs.
We see Uraraka reading a letter written by Deku. The letter thanks her for everything, detailing that Deku felt he needed to explain his secret to all students in Class A. He admits he is naturally quirkless and his power was passed down to him from All Might. Shigaraki and All For One are coming after him, Deku writes, so he must leave the school for everyone’s safety.
Panels reveal that Deku left similar explanation letters under all of his classmates’ doors. The narrator states that if you define a hero as someone willing to suffer in silence, then who’s there for them when they’re in pain?
The chapter concludes with Deku, standing upon a building with Gran Torino’s yellow scarf. It’s stated that in April, Deku left the Hero Academy.
So that’s the answer. Deku does tell everyone about One For All. He admits the truth about his power in a series of letters he left behind for his classmates. The letters explain that he must flee the school for everyone’s safety, as Shigaraki and All For One are coming to steal his quirk.