In his couch, Midoriya Izuku sat mourning the deaths of his friends. On the other side of the door was a world that he couldn't face, not yet. No. 1 Hero he might be, but the world, his career, his life, could wait. His childhood friend, three of his best friends, and his former teacher. Gone. Was it really just last week that the former Class 1-A had met up and reminisced about their (almost, not quite) care-free high school days? Was it really last month that Shouto had hosted their bi-monthly movie marathon nights at his house?
Curling up into a ball, Izuku sobbed into a pillow. His friends, his pillars, gone forever. He had read somewhere, long ago, that Death is but the next great adventure. A great and great adventure Death might be, but he mourned the death and loss of some of his greatest lights. In that moment, on that old, worn-out couch, in his ratty sweatpants and oversized T-shirt that he had stolen from Kacchan just two weeks ago, he swore that he would protect the last one.
Uraraka Ochako.
Two weeks later, still dazed with grief, the No. 1 Pro-Hero Deku, was killed in action, trying to protect a child from the last vestiges of All for One's might, his last legacies, hell-bent on causing as much destruction and terror as possible before being taken down. Less than five hours later, the No. 7 Pro-Hero Uravity died in a fire, caused by a villain who had carried and nursed a deep grudge against the No. 3 Hero, Shouto. Now that he was dead, one of his closest friends seemed appropriate to take out all the rage on. Dabi was apprehended fifteen hours later. Uravity's body was never recovered. Two years later, Uraraka Ochako's sister, Miyamoto Hanako, gave birth to a healthy baby girl, whom she immediately named after her deceased sister.
The world mourned. Slowly, slowly, the cogs in the clock of time creaked on. Centuries flew by. Quirks eventually disappeared nearly altogether, with the last Quirk-holder going into hiding. Years later, one Hinata Shouyo discovered that the reason he could jump so high wasn't just because of training. His father was a descendant of the legendary hero, Uravity, and he had inherited a mild anti-gravity quirk and involuntarily activated when he jumped. Just days before, one Kageyama Tobio unearthed his family's odd history. Their line was descended from a hero, the Jet-Black Hero, Tsukiyomi. How fitting that the descendants of two powerful heroes who had gone to school together and forged deep bonds met. Hinata Shouyo and Kageyama Tobio met in high school, played on the same volleyball team for almost 8 years, and died together in a car accident.
Thousands and thousands of years later, Quirks had been rediscovered by a woman who claimed herself a goddess, one Otsutsuki Kaguya, and the river of fate wound its way through the souls of heroes.