I have seen something else under the sun:
The race is not to the swift, or the battle to the strong,
nor does food come to the wise, or wealth to the brilliant, or favor to the learned;
But time and chance happen to them all.
It took a while for Izuku to really get his Quirk. He spent a painfully long time unaware of the catch- he still regretted that.
Sure, he passed the toe joint test and everything, but his Quirk seemed to be taking its sweet time to show up when he was younger. Back then, it was relatively subtle, only just starting to manifest itself, so meager that it would be hard to notice.
His mom probably started to notice around when he was dropping off fistfuls of coins he picked up on the way to school each day- Izuku just thought he was lucky. And yes, he was. Unnaturally so.
At first, they figured that was it. Izuku had, by some whim of chance, had a Quirk that attracted good fortune to him. Sure, it wasn't as strong as Bakugo's or anything, but there was some use to it! Izuku could make something of it!
Still, his luck wasn't perfect, unless his quirk somehow considered confrontations with Bakugo and friends a good thing. (They weren't.)
"Your quirk's so fucking weak it's hardly better than any quirk at all!" Bakugo towered over him, one hand clenched painfully tight on Izuku's shoulder as the other palm sparked and popped.
Before Izuku could mumble some response, Bakugo continued. "A useless quirk for a useless Deku!" Izuku swore that his uniform was starting to smoke…
Desperately wishing that Bakugo would just go away, Izuku felt something flow from him, some sort of power leaving him… and at the same time, Bakugo's quirk backfired.
By some freak accident of chance, a trail of nitroglycerin sweat was caught by an otherwise unimpressive spark- leading to a brilliant heat and a blast of smoke, punctuated by Bakugo crying out in pain.
Izuku turned and ran when he saw blood.
Izuku could feel it now, a wretched ball of misfortune sitting inside of him, waiting to be poured out upon someone. Someone like Bakugo.
He got the feeling that he had lost a significant chunk of it hurting Bakugo- bad luck like that was a lot worse than the many minor incidents of good luck he had experienced over the years. However, some still remained, hanging like a weight inside him.
Slowly, cautiously, he let it leak out, a miasma of bad luck forming around him…
He had come to realize that, perhaps, miring himself in misfortune was not the most stellar of ideas.
In no particular order: he ran out of phone battery, gotten lost, had his clothes thoroughly ruined by mud he had fallen into… he was also fairly sure there were still twigs in his hair.
Collapsing on a park bench, he held his head in his hands and tried to think. A bit about where exactly he was- mom would be worried sick- but more about his Quirk.
Sure, he understood that powerful quirks had capacity to harm. Any one of the greatest heroes would make a terrifying villain… but recognizing, clinically, that a quirk could do damage was different from hearing Bakugo howl and seeing him clutch at his bloodied arm.
Wait. Was Izuku going to get in trouble for using his quirk? Like, everyone knew he was lucky, so would they connect a 'freak accident' to him? Would they arrest him for this? Would he ever be allowed to become a hero?
"Are you alright?" He hadn't even realized someone had sat down next to him.
Ibara Shiozaki was taking a jog, as part of preparing for hero work. Being blessed with a quirk and not working to facilitate it… well, that would be wasteful, wouldn't it? It was, she figured, her duty to make the most of this power by helping others, although the hero licensing was more a means to the end- there was no reason to put off help she could provide right now.
So when she saw an unfortunate looking boy sitting on a park bench, his clothes caked with mud and his head in his hands as he muttered up a storm, she approached. Comforting the afflicted was a work of mercy, after all.
"Are you alright?" Perhaps not the best opener- she figured that he probably wasn't- but it was something. Better than walking past the young man without so much as a word.
"I'm…." he sighed. "What would you do if you realized your quirk was a lot more dangerous than you thought?"
"What do you mean?"
"My quirk… it has a catch." The boy said. "A catch that can really hurt people."
"Are you going to let it, then?" She asked rhetorically. "When the time comes, people will judge what you do, not your quirk." Perhaps that was a touch optimistic- some quirks just had stigma- but she was smart enough not to bring that up.
"I suppose, but…"
"Your quirk will never do anything, good or bad, if you just sit here navel-gazing."
She smiled at him. "You're certainly not going to become a hero if you just spend your days sitting around."
The girl- Ibara Shiozaki- made a good point, Izuku thought. He wasn't as strong as he could be, and he was certain there'd some sort of physical test to get into UA…
So Izuku found himself doing morning jogs with Shiozaki, bright and early every morning- except Sunday. Then they did evening jogs.
On one of said jogs, they found themselves passing by a particularly junk-covered beach.
He thought he would die of embarrassment when he slipped not once, but twice on the steps leading to UA. He was trying to bleed any extra bad luck he had on him, and it was only thanks to a nice girl by the name of Ochako that he didn't eat pavement.
...
He clenched the ball tightly in his hands, his grip vice-like. Letting out of a burst of good luck, Izuku could feel the wind starting to pick up…
Izuku swayed and tumbled to the floor as a tremendous amount of bad luck poured out of him and into the Nomu.
He crumpled, his vision fading to black as the Nomu let out a howl of agony...
The Nomu was empowered with regeneration far beyond anything natural, billions or even trillions of cells being made in seconds…
Unfortunately for the Nomu, one of its cells made the most minute of errors while dividing. An adenine instead of a guanine, perhaps, or maybe a cytosine where a thymine should have been. A quirk of chance led to a mutation, a mutation that led to a cancer cell.
In anyone else, this would be a long-term concern, but the hyper-regeneration which saved the Nomu from death doomed it, letting cancer spread at a tremendous pace.
By the time All Might had arrived, the Nomu was little more than a disquieting tumorous mass.
When Izuku woke up, a dark figure hung like a specter near the end of his bed. A bit of squirming revealed the figure to not be some angel of death, but rather Aizawa-sensei. Although a destroying angel looking like him didn't seem that farfetched…