Tsuyu, who had spotted his boat adrift near the shore

"Can you hear me, kero?"

Izuku's eyes snapped open. He groaned, every part of his body feeling sore. "Y...yes"

Wait...That wasn't his voice. He slowly pushes himself up to a sitting position to try to look himself over...or at least, he tried, but after probably more than a week ****, it was honestly inexplicable that he was awake at all, and his arms couldn't muster the strength to lift himself.
He slips back to a prone position, opting instead to tilt his head forward...but all that he could see was two massive...breasts? under a vaguely transparent wet shirt.

The effort of the attempt to rise though, had sent a wave of dizziness through Izuku, and it's too much for his drained, weakened body. He feels himself blacking out, having just enough time to process part of the end of the girl's next sentence amidst the dizziness: "...the hospital, help is coming, kero"

Blackness took him again as he slipped back into unconsciousness.

The next time Izuku woke, it was much less unpleasant, though still not great. The soreness was still there, and he still felt weak, but it wasn't so overpowering anymore, and it didn't take long for his analytical mind to piece together why: He was in a hospital bed.

That much made sense, if he was going to wake up at all. He must have missed the island itself and continued past it. He'd aimed his course such that that would send him back to a shoreline. Someone had found him...a girl?...his memories were fuzzy but he remembered something of the first time he'd awoken.

This time, he took things more slowly. First, figure out his current condition and surroundings better.

Turning his neck took effort, with how stiff it was, but it wasn't nearly the agony of trying to move that first time. The room seemed fairly standard for a hospital, but he couldn't see directly forward past the swell of the blanket over his chest...

So that hadn't been a dream then. With some effort, Izuku managed to lift and maneuver arm enough to pull the blankets off to one side, and reveal that, despite the meager attempts of the hospital gown to hide them...yes, there were a pair of enormous breasts attached to his(?) chest. He blindly fumbled with the controls on the side of the bed, finding them after a moment, and managed to lean enough to see which was which and raise the back of the bed up, tilting himself into a near-sitting position, and pulled the blanket fully away to reveal as much as possible, accidentally sending it to the floor in the process.

He was shocked...he'd become a girl! At least...that's what it seemed. Everything Izuku could see was decidedly feminine...arms, legs, breasts. He tested his voice. "Hello...hello." His voice too.

But there was one thing that was decidedly not. In fact, it was more manly than it had been before...his huge, thick, 10 inch cock, currently erect and jutting up and out of a gown clearly not meant for "her" new body shape. "Oh my god", she muttered under her breath.

"You're awake, kero!"

If Izuku hadn't been so weak, he'd have jumped out of the bed and hit the ceiling. As it was, his neck swiveled somewhat painfully fast to the opposite side of the room from where he'd been looking, to the source of the voice...a young adult woman seemingly having been napping in a chair in the corner, with dark hair and a somewhat quirky appearance...but cute.

"My name's Tsuyu Asu...oh my god!" Her eyes widened as she caught sight of Izuku properly, most specifically her erection.

Izuku's hands jerked the gown down over her erection, hiding it from view, mostly, but it was a barely effective effort.

Blushing heavily, Tsuyu hopped up and picked up the blanket from the ground. Izuku assumed she was going to return it, but as she leaned down, her eyes never left the bulge in her gown, and there was a period of several seconds where she merely stared, loosely holding the blanket.

"Um...did you...find me?" Izuku broke the silence.

Tsuyu startled, and blushed more, tossing the blanket over the lower half of Izuku's body. Even that was minimally effective, given the huge tent that they both knew exactly what was beneath, but it provided at least the illusion of decency.

"Y-yes. Your boat drifted ashore. I was watching it at first, kero, but when it got close it rolled as it hit shore from the waves and wind, and I felt like I had to check to make sure no one was onboard...I pulled you out of the cabin and back to shore, and called an ambulance. "

"Thank you..." Izuku said, softly.

"I should probably let someone know you're awake, but if you don't mind me asking, what happened?" Tsuyu cocked her head to the side with a finger by her mouth, clearly curious.

"I..."