Foundational Hero Studies end and Class 1-A return to the locker room to change. In the boys' locker room, Minoru finds a finds a hole in the wall and becomes excited that the hole will let him see the girls' locker room. Tenya reprimands Minoru for his behavior, but Minoru decides to look through the hole anyway. Minoru excitedly takes a peek through the hole. However, Minoru's eye is stabbed by Kyouka's earphone plug. In the girls' locker room, Momo, Tooru and Mina are annoyed with Minoru's antics and thank Kyouka for stopping him.
After getting changed into his school uniform, Izuku heads to the Break Room to meet with All Might. All Might tells Izuku to lock the door and then apologizes to Izuku for not being at his side during the Hosu incident, to which Izuku replies that he doesn't have to apologize. All Might says that Izuku's blood was ingested by the Hero Killer,reminding Izuku about One For All transfer and inheritance method, causing Izuku to panic (thinking that One For All is in Stain's possession). However, All Might tells Izuku that he still has One For All because One For All won't be transferred to a new recipient unless the user wishes it, thus One For All cannot be forcibly stolen, although it can be forcibly passed on. All Might tells Izuku that One For All is a special Quirk and begins telling Izuku One For All's origin. All Might says that One For All is derived from a Quirk that has existed since the beginning.
All Might says that long ago during the Quirk phenomenon, society had not adapted to the idea of having Quirks which caused an age of upheaval to arise; a man possessing a Quirk called All For One (a Quirk that can steal Quirks and grant them to the user or another) stole many Quirks and used his new overwhelming power and influence to gather and unify people under his command. The man used the people he gathered as pawns for his plans which allowed to take over Japan and made himself its evil ruler. Izuku says that he has heard rumors but this story is not in any textbook, causing All Might to reply that underground dealings are never recorded in the textbooks. Izuku asks how this man is related to One For All. All Might says that All For One can grant Quirks but those who were not able to handle the strain became brain-dead like Noumu. All Might explains that there were cases for those who did survive the procedure where their Quirks mutated. All Might tells Izuku another story; the man (who would eventually become Japan's evil ruler) had a Quirkless younger brother; the man used All For One and forcibly gave his younger brother a Quirk that stockpiles power. However, the younger brother already had a Quirk, a Quirk that can transfer itself to others. The younger brother's Quirks (one that stockpiles power and the other that can transfer itself) merged and became One For All.
All Might notes the irony that justice was born in the bowels of evil. Izuku says that it is impossible for the man who ruled Japan in the distant past to be alive. All Might theorizes that the man stole a Quirk that stopped his aging or a Quirk that granted him immortality. All Might explains that the younger brother, whose Quirks became One For All, fought against his older evil brother but could not defeat him. The younger brother decided to pass on One For All to the next generation so that one day it will accumulate enough power to defeat the older brother's All For One; All Might says that he was finally the successor that defeated the older brother, or so he thought. All Might tells Izuku that the man possessing All For One has returned and is leading the Villain Alliance. All Might finishes his story by saying that One For All is a power that is meant to stop All For One and that Izuku will also have to confront the older brother. All Might apologizes for giving Izuku so much information. Izuku says that whatever task All Might gives him he will accomplish no matter what as long as All Might is by his side. All Might isn't able to bring himself to tell Izuku the truth and thanks him instead; All Might isn't able to reveal that he probably won't be by Izuku's side when the time comes.
During class, Shouta tells Class 1-A that they will be going to a forest lodge during the summer break. However, Shouta warns his students that if any of them fail to pass the end of term test, then they will be stuck in remedial school.
Elsewhere, a man is surprised that the Hero Killer Stain was captured but is still happy that things are going as he has foreseen. He exclaims that Tomura's position is to supervise and unify the new villains who have come to join the Villain Alliance. The man's doctor expresses doubt if Tomura can do his job and says that if the man stepped in things would be proceeding faster. The man asks the doctor to patch him up faster. The man reveals himself to be Tomura's sensei (the man who possesses All For One) and says that he will let Tomura do all the hard work so that he may become his successor as Tomura was born to do so. Sensei tells All Might to rejoice in the "transient" peace while he still can.