Work Text:
"And you did it." With Shigaraki's surrender, Deku seized back his Quirk, One For All. But something strange happened: With All For One's desperate cry for his brother's ember to come back, to be with him, the All For One Quirk tagged along for the ride, and Deku gained that Quirk, too. The two Quirks were finally reunited! Meanwhile, the Quirkless spirit of All For One got dogpiled by the spirits of all the Quirks he'd ever stolen, before they too joined Deku's mindspace.
Almost without consciously wanting to, his physical mouth intoned, "All For One, and One For All!" As Deku watched in awe, the two Quirks merged into a new Quirk, All For All! First, everyone who had a Quirk joined him in his mindspace, then everyone who used to have a Quirk, then everyone who was Quirkless, and finally, everyone who had died since the first Quirk had awakened. Sensing the strain on Deku's body, everyone joined hands, both spreading out the mental load and granting him their mental capacity. "Overhaul. Rewind." Nighteye, Star and Stripe, Toga, and everyone else who had died during the last few days of battle was restored back to life! Finally, everyone who was hurt, had terminal diseases, merely had a sniffle, or wanted to have their gender match their sexuality, was Overhauled! Needless to say, quite a few people were glad to lend their efforts to restore All Might back to his Golden Age body.
Deku wasn't done, yet. "Quirk Bestowal." Hawks, Star and Stripe, and Ragdoll have their Quirks returned to them, and those with damaged Quirk Factors were also healed. Those people who despised their Quirks and the criminally insane, had their Quirks bestowed upon those who would most appreciate them. Toga was one of those who willingly gave up her Quirk, and recieved a gentler Copy Quirk in exchange. Doctors and plastic surgeons around the world recieved copies of the Overhaul Quirk. Counselors and therapists got Telepathy, Empathy, and Hypnosis Quirks.
"Alchemy." Shigaraki's original Quirk, before All For One took away half of it, rebuilt and repaired structural damage, vehicles, and countless other physical things, setting things up for a return to normalcy. "Search. Warp Gate." Lost things were found.
"Telepathy." With everyone who had ever lived and died in Deku's mindspace, inevitably people would look around and have questions. And everyone was eager to spread the news: All For One, Shigaraki Tomura, and the League of Villains had been defeated. Historical figures hashed out opinions and facts with those who wanted to know. Families were re-united, and closure was attained. Frauds were exposed, and promptly promised to turn themselves in, both for incarceration and therapy. Scientists collaborated, and made new discoveries. Soul-mates met, and made arrangements to meet in real life. With the speed of thought, World Peace had been achieved. Deku released the mindspace, and promptly slept like a rock for the rest of the day.
And everyone lived happily ever after.