A blowjob, of course. Can't leave a mess for the doctors.

Tsuyu pulled back the blanket, revealing the still hard, now throbbing, slightly purple erection that was no longer even pretending to be covered by her gown, and a pair of lemon-sized balls.

O-oh. Wow." Tsuyu leaned in close and inhaled, seemingly completely distracted by the cock in front of her. Her tongue, which had hung partway out of her mouth a few times during this conversation, extended and wrapped around the shaft, and Izuku groaned. W-what? She didn't think she'd last very long in this condition.

That prediction was solidified when he noticed that Tsuyu's hand hand had slipped down her pants and was rubbing herself. Izuku's blush deepened as she felt herself beginning to boil over almost immediately. "I...I'm..."

Tsuyu apparently somewhat expected this, as her head lurched forward and enveloped both her entire cock and her tongue wrapped around it, and that was the last straw, Izuku exploded, with probably more cum than he'd emitted his entire life combined before filling Tsuyu's mouth. She had no trouble keeping up with even the heavy flow, and swallowed in a few gulps.

She was blushing almost as much as Izuku as she pulled away, leaving a rapidly deflating much more reasonably sized cock behind. Even her balls looked somewhat smaller. "I wouldn't normally...I just...kero...that looked painful and embarrassing... and I didn't want to leave a mess..."

She'd blushed even more and motioned to the door. "I'll go let someone know you're awake."

Hours later, Izuku was certain that she'd had more exams today than the rest of her life combined. The doctors weren't sure how she'd recovered so quickly from the radiation, or why it had had this particular effect, but what was certain was that her plan had...well, it had done something fundamental to change her. She had a quirk, but didn't yet know what it did or how it worked.

Tsuyu had stayed a while longer and just talked with her in between rounds of doctor's . It wasn't every day you found someone nearly dying of radiation on the beach, or having spontaneously changed sexes, she supposed, even for an aspiring hero, as he found out the girl who'd saved him was already going to be a student at UI, though classes hadn't yet started. Small world...

Anyway, what the doctors discovered was numerous oddities that added up to a definitely quirk factor being present, but the exact details weren't yet clear. Izuku's new body was mostly feminine, with all the associated internal organs, but also both sets of genitalia...and both appeared to be very fertile. She'd slipped easily into this new identity...She supposed her identity had mostly always just revolved around wanting to be a hero...her gender wasn't something she'd expected to ever be questioning, but now that her body had changed, she realized that she wasn't really attached to her previous body nor the labels that went with it. Her pheromones weren't normal, nor did it seem normal how much attention the doctors and nurses seemed to give her body, and when she popped a second boner as soon as an attractive female nurse entered the room, despite Tsuyu's "help", it became clear that her libido was higher than it had ever been before as well. Beyond that, it was almost completely unclear how much her new quirk could do. It certainly changed a few things, and opened up some career options, but none of them seemed appealing. How could it help her with becoming a hero? She could maybe see seducing a villain to trick them, but that would only work on some, and the first time it didn't, she'd be dead.

Has she really come this far only to get a quirk that was irrelevant?

This was what Izuku worried over for the rest of the night...unable to sleep even once the tests had died down for the day. Tsuyu had left, but had given Izuku a number to get in touch with her. She'd say they were friends, though they didn't know each other that well yet, and Tsuyu had seemed interested in meeting up again. It wasn't until two mornings later that life presented a new development that shifted the course of Izuku's life even more, when a visitor showed up at her hospital room.