An opportunity.

All Might proceeded to have them all get dressed in their commissioned Hero Uniforms, and they all went out to meet him once they did. (Same as canon.) Izuku found Ochaco's form fitting and Momo's revealing costumes quite enticing. Ochaco wasn't even embarrassed about it, giving him a discreet twirl in it while only he was watching.

"...are you some kind of exhibitionist?" Kyoka asked Momo, pointedly ignoring Mineta practically drooling at the sight of Momo's outfit.

"Yes, but that's not the reason my outfit is like this. My Quirk needs exposed skin to work with, so me being an exhibitionist is a happy coincidence," Momo stated without any hesitation or shame, leading to some gaping from other students at her level of confidence in admitting that.

All Might proceeded to lead them to a training ground, one with multiple run down buildings, explaining that the class would be divided into ten teams of two, and five matches would be held, between a team playing villains, and a team playing Heroes. Of course, he was reading his explanation from a script.

"...is he actually reading from a script?" Iida asked, bewildered, wondering if his opinion of the Number 1 Hero should take a hit from this.

"Cut him some slack, he's an amazing Hero, but this is his first time teaching," Izuku defended his mentor and idol. "If anything, him preparing a script and having it on hand shows that he's committed to getting this right."

"...I see, good point," Iida conceded. All Might was quite thankful for Izuku making such a statement on his behalf... The befuddled states of the students had made him a little self conscious.

"So, any questions?" All Might asked, recollecting himself, only to get bombarded with them, most concerning being Bakugo's question about how badly they could hurt their opponents.

In response to that, Momo, while looking directly at Bakugo, asked, "Are nut shots allowed?" Bakugo actually showed a flicker of fear at that.

After All Might answered all the canon questions, he looked at Momo and said, "While all is technically fair in the real world field, I'm going to go ahead and ban any deliberate... Low blows like that." He shivered at the thought. "You certainly picked a feisty one, Young Midoriya."

"Probably for the best anyway... If it was allowed with Bakugo, it'd be allowed with all the boys too, and we don't want any harm coming to "Little Izuku,"" Ochaco whispered to Momo.

Izuku, close enough to hear them, blanched at the thought. Momo also grimaced. "...fair point," she grumbled, but she was still disappointed. She still hoped for a chance to kick Bakugo's ass though.

Once All Might explained all the rules about how to win for both sides, the Villains basically having to avoid capture or prevent a fake bomb from being secured by the Heroes for fifteen minutes, he then announced that the team selection would be done by lottery, and matchups by a second lottery. When Iida questioned this, Izuku once again stepped in to explain a lot of random things, including Hero team ups and opponents happened in the real world, putting Iida's concerns to rest.

Momo meanwhile, had an idea, and whispered to Izuku, "You know, Master, I could easily influence who you get teamed up with with a well worded wish... Like say, if you wished for the most likely person you're attracted to to join your harem to be your teammate..."

"Isn't this supposed to be random though?" Izuku murmured back.

"Meh, it still is, but guarantees potential romantic chemistry, even if not combat chemistry, so it's only kind of cheating..."

"...alright, I'm in," Izuku hissed, letting Momo have a little harmless fun every now and then, and he had to confess, expanding the harem if there was another consenting partner in the class appealed to him.

(Side note, the story will split here. One branch will be Straight Izuku, the other branch will be Bi Izuku, and the partner in question will be female in the first branch, male in the second. I'm mostly going to work on the straight branch though, unless enough people tell me to do more with bi. While I'm bi myself, I also want the main branch to appeal to as many people as possible, so I'm fine either way. That's kind of the main advantage to bisexuality, lol.)