Hit by a strange quirk, Izuku finds himself trapped inside a dream where superpowers only exist in comic books, he's a normal high school student, and All for One is his father. He can't possibly be related to a villain…right?
Izuku is a half-demon mercenary who has survived on his own ever since he lost his mother as a young child. In the middle of a job, Demon Lord Hisashi identifies Izuku as his long-lost son. Izuku scorns this demon who wants to baby him. Hisashi has no idea how to handle a son with the cherubic face of a teenager, the foul mouth of a soldier, and a murderous vendetta against demons.
As quirk development marches on, All for One would like to present his new and improved vault.
Toshinori is the son of Nana Shimura and All for One, the product of a one night stand. His parents may hate each other but they absolutely love their son Toshi. The custody battle only intensifies after Toshinori marries Inko. Both grandparents are determined to win the affection of Baby Izuku.
All for One finally steals One for All. Unfortunately for him, Izuku and the vestiges' innate goodness is contagious. Contagious in the sense that they keep taking over his body and using it for heroism.
All for One wanted a son, so he claimed a different price from the Aoyamas.
All Might and Izuku travel back in time, rescue child All for One and First, and sort of become villains.
All for One sent his son Neito Monoma to U.A. as a spy. Neito has his own plans.
After their deaths, All for One and Yoichi reincarnate in a world with no quirks. Their neighbor Izuku is a salaryman with a fishy family background, who steps up to look after two neglected kids.
Shouto Todoroki has prepared the ultimate April Fool's Day prank: convince Izuku that All for One is his long-lost father.
When All for One sends Nomu back in time to kill the past One for All holders, adult hero Izuku chases after them. Izuku must fight his way through time to save his predecessors, starting with stopping Second from being assassinated before he can ever let Yoichi out of the vault and ending with rescuing a young Toshinori Yagi living on the streets.
Izuku gets swapped with his eldritch abomination counterpart from another universe.
In an alternate universe, Touya Todoroki stayed a loving and protective older brother even after he became Dabi. Unfortunately, what Dabi would call protecting, most people would call kidnapping.
After being hit by a strange quirk, Izuku finds himself holding two white-haired brothers who claim to be from the past. When All for One takes an inexplicable interest in the time-travelers, All Might volunteers to protect the adorable brothers. OR: All for One loses his shit after his younger self and his long-dead brother travel forward in time and get adopted by All Might.
The kitsune lord All Spirits In One has an ingenious plan to lure his rebellious little brother back home: cute pictures of his newborn kit.
All Midoriyas are heavy criers, including those who married into the family or were adopted. It might be a quirk, a mutation, or a curse. Tomura is about to experience the waterfall tears, because his sensei is married to Inko Midoriya and the father of one annoying but adorable brat, Izuku Midoriya.
When Izuku was four years old, he made friends with a sickly little boy at the park. His friend's older brother had the same first name as his father. Neither of them knew much about current events. Izuku happily provided the older brother with information about politics and stock market movements. (Izuku doesn't know he has a quirk, but his father has known for a very long time.)
During the dawn of the age of quirks, All for One wiped his younger brother's memories and de-aged him. Although Yoichi's friends succeeded in rescuing him, whenever he reached age fifteen, he regressed to infanthood again. With no way to cure him, they hid him from his demented older brother using a series of caretakers. The current incarnation is named Izuku Midoriya.
Izuku gets hit by a quirk that turns him into a green corgi puppy. Tomura adopts him on sight.
After Izuku's demented supervillain father locks him up inside a bank vault, he discovers that he's not alone. All for One has been holding Yoichi captive since the dawn of the age of quirks.