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Even his “cold” shower was uncomfortably warm.
Izuku groaned to himself as he made his sweaty, sore body enter the steam of lukewarm water. It was, admittedly, still way cooler than he was, and very much a relief for his aching muscles after training with All Might all day. Which was something he was only able to do because it was so hot that his school had to shut down. Izuku really wanted an arctic lake to jump into.
He'd been safe about it. He wore sunscreen, drunk plenty of water… Well, it was actually rescue grade energy drink that All Might brought, but the point still stands. His hands were mildly blistered from the heat of moving all that heavy, and often metal or plastic, trash, and he was incredibly exhausted, but he had been safe.
There was, sadly, a point to all this. Heatwaves are a very active time for heroes because heat stroke is the leading cause of quirk mutations and especially maladaptive quirk mutations. The overheating causes DNA and other proteins to begin doing weird things, and it puts a lot of stress on the body. It can even cause quirks to manifest forcibly, but it's rare and there have only been a few documented cases of it.
When Izuku first learned that fact, he thought that maybe he could be one of those lucky few, but thankfully for him he encountered All Might. As it turned out, every single quirk that has manifested due to a heat wave has been maladaptive, crippling or even killing whoever had it. The only time someone with a quirk like that even led a normal life was because the stress of their body dying to their quirk caused a different quirk mutation that saved them.
Izuku pushed that thought from his mind. It had quickly become a common summer nightmare for him when he found out about it. While he knew it was unlikely, the thought of manifesting a quirk that ended up killing or crippling him in some horrifying way was—
“Ert!” Izuku grunted suddenly as he was pulled from his thoughts by a painful jolt from his crotch.
He looked down at himself, and saw that his cock was completely erect. He's seen it get hard in the shower before, but it wasn’t usually this bad. A second, stronger jolt hit him and he was brought to the floor. He got up on one knee and turned the shower off to prevent himself from slipping as easily and so that he could yell for help.
The next jolt sent him to the floor, and he pushed himself up against the wall since any kind standing seemed to be courting disaster.
“Wha- What is happen- NHG!!”
The sweat he had just barely managed to rinse off returned with a vengeance, and Izuku realized with dawning horror that he couldn’t hear the air conditioner. The bathroom door had been open when he came in, so it was being cooled by the hallway's mini split, but a quick look to the ceiling confirmed that the bathroom's unit was off, and Izuku had no way to turn it on.
He was trapped, immobile, in the most insulated room in the entire house, during a forty degree heat wave, without air conditioning. He was already dealing with mild heat stroke symptoms when he walked in.
He tried to force himself to get up, but another jolt brought him back down. The constant spasms, crippling heat, and pre-existing exhaustion were all sapping away his strength. Tears mixed with sweat stinging his eyes as Izuku was confronted by the very real possibility of dying here, alone in his own shower, with the most strangely intense erection he had ever had.
He tried to get his arms above his head to reach the shower handle. He grunted with effort as his shaking arms reached for it, desperate for the small amount of cooling the water would provide.
Jolt
“AHHGG!!” Izuku screamed as the electric shock coursed through him.
His arms fell uselessly to his sides. He could barely move them. He was so, so tired. It wasn't fair. He had worked so hard to get strong enough to wield All Might's quirk, but the only things his bulging muscles were doing were making him hotter and weighing him down. He was dizzy, nauseous, and completely exhausted already, but the room just kept getting hotter.
He barely reacted to the next jolt, just wincing before glaring at his cock. Screaming took too much energy.
The jolt after that was a different matter entirely. He yelped in shock as his balls clenched, and hissed in pain as scalding cum shot from his dick and splattered onto his stomach. It thankfully mixed with his sweat and rolled off of him, but it had legitimately burned both when it hit him and as it came out.
Izuku could both feel and hear his balls churn as they prepared another load. He whimpered pathetically. It seemed that whatever horrible quirk he was developing was intent on torturing him as he boiled alive.
The next jolt arrived sooner than expected, and Izuku let out a pitiful excuse for a scream as much thicker and denser cream hit him in the chest and face. It stuck to him like glue as his skin blistered and burned underneath. He could already feel the next round filling up his balls.
The next jolt came even sooner than the last, coating his stomach in burning, tar-like sludge. It only took a few seconds for the next jolt to scald his face again, and the one after that hit him just over a second later and left him coughing and choking as it went straight into his dry, cottony mouth.
Not even a second later, he erupted again. Then again. Until it started to become a high pitched hum of electricity that served to fuel a violent geyser. His shaking muscles spread it around him, and he was being buried in viscous liquid.
He was so much weaker now. He could feel his blistered skin shrinking as his muscles were being digested to make more spunk. His bones were becoming like jelly as well, and he was soon to be a worthless pile of overheated and likely damaged organs.
Izuku laughed weakly, more than a little delirious from the heat and the constant orgasm. He was going to die here. He'd wasted All Might's time, and he wasn't going to receive One for All, or go to UA, or become a hero. Instead he was going to die to a maladaptive quirk that manifested during a heatwave and was rapidly converting his flesh into scaldingly hot cum.
His arms and legs had been practically emptied out by this point, and Izuku could hardly feel them as his skin dissolved. Though, perhaps “dissolved” isn't the right word, it wasn't like the pool of semen had become caustic or caustic. It was as if Izuku himself had reached his melting point.
Finally, Izuku was met with relief as his cock stopped erupting and grew numb. He opened his eyes to look, but two large globs of thick liquid were released instead. He couldn't hear anything either, and could feel a thick fluid trickling out of his various orifices.
Then his sense of touch was lost to him, and Izuku was left alone with his thoughts as his body flowed thickly down the drain.
~~~
Three weeks later, the heat wave had long ended, and Midoriya Izuku had still not been found. A lone figure looked sorrowfully across a breach of trash. It wasn’t because of the damage to the environment, but because he couldn’t find his successor. Yagi Toshinori hadn’t known Midoriya Izuku for long, but he knew he was the right choice.
Suddenly, a wave crashed over the beach. That alone wasn't all that surprising, but it was what was left behind that really caught Yagi’s attention.
The water currents near the area sent just about anything floating in the sea onto Dagobah beach, and this time it sent a figure that was almost familiar to Yagi. The body was wrong, too pale and the wrong shape, and the hair was too long; but Yagi would know that hair anywhere, even when wet.
He rushed over to them, and at his touch they began to cough. A glimmer of hope sparked in him when they flipped themselves over, clearly very exhausted, and looked at him, recognition in their bright, emerald eyes.
“All… Might…” they said, before falling unconscious.
Yagi let himself cry tears of relief. For he was not here as his hero identity of All Might, he was here as Yagi Toshinori. There were only a handful of people who knew the two were connected, and only one of them is a missing person with green hair and eyes.
Midoriya Izuku had been found.
~~~
Izuku had gotten so incredibly lucky.
He walked out of the hospital in a daze. He was wearing a bunch of All Might merch that his mentor had brought in, but he'd really need to redo his wardrobe. Nothing he owned would fit him anymore.
Externally, Izuku looked pretty normal. Different from before, being a couple inches taller, more muscular, and far too pale, but he still looked like a normal person.
On the inside, he was completely alien. Izuku's body had almost nothing human about it internally. His hair and nails were the same as before, but his skin went all the way down and functioned as his muscles. It was connected directly to his bones, which also had a sort of muscle in them that told them when to lock up and when to be flexible, which was important as Izuku didn't have true joints.
His eyes were structured mostly the same, but they didn't have a blind spot. This was because they connected instead to Izuku’s body fluid: a semi-solid, dense, white gel that served as Izuku’s blood, nerves, brain, digestive system, reproductive organs, and reproductive cells. It was made of highly modified sperm cells and spermatic fluid, which made Izuku basically a fleshy bag of cum.
All and all, Izuku was just glad that he didn't die. All Might was even still giving him One for All, and says he’s strong enough to handle it.
Izuku had gotten so, so lucky