They start working out the system for harem building.

"Okay, if we're going to do this, let's workshop it," Izuku said, getting scrap paper from his desk and a pen. "First off, deciding who and when we invite to our dynamic. I'm going to insist on getting to know people beforehand but the question is, how long should we have as the general guideline?"

Momo pouted slightly, before considering. "...is two weeks enough?" she asked.

"...a bit fast, but fair, we'll call that the bare minimum before we start to ask the question of whether we invite the girl in question," Izuku remarked. "Then there's the question of how much we tell them before the invite. Definitely not being the fact you're my girlfriend from them."

"Of course not... I'll just make sure to mention we're in an open relationship to make sure that doesn't make them lose interest~!" Momo giggled, once again making Izuku blush.

"That might be a bit much..." he said hesitantly.

"We can always tell people it's my idea if that helps!" Momo replied. "Not like my parents would mind too much either."

"How do you know that?" Izuku asked. "Have you ever asked them?"

"I just straight up told them shortly after becoming a genie that I was bisexual, and would try to talk you into dating multiple girls, and they were quite cool with it. They're pretty open minded."

"...oh..." Izuku blushed.

"Alright, now, as for how we extend the offer..." Momo mused. "Perhaps visit them in a lucid dream? One where they're fully in touch with their own sexual side... If they accept, then we got ourselves a harem member, if not, they simply won't remember the dream."

"Right, I suppose that works... But what about the dynamic? Are you just going to want them to be my sex slaves too?" Izuku asked.

"Nah, not necessarily," Momo replied. "The dynamic will be whatever you and she agree to. An equal dynamic, perhaps she's a switch, and will let you dominate her, but she'll get to dominate me, whatever works for you both. And obviously, we'll pitch the fact that I'm a sex genie and can really enhance the sex life of all involved."

"Okay. Can we agree that anyone attached is off limits?" Izuku asked.

"We could always agree to get the boyfriends in the dream. Maybe we'll be able to get them to agree to share in exchange for a few wishes made in their behalf to enhance their sex life. Assuming both the girl and the guy are okay with it," Momo suggested. "We're not the only ones who need to have an open relationship."

"...right, fair enough. I guess none of the potential harem should have any rules against dating multiple guys themselves. That would be hypocritical of me, given I'm actually going through with this scheme of yours," Izuku replied.

"Exactly. Sex isn't something that should be limited by societal expectations after all, it should be freely shared between all consenting adults," Momo nodded fervently. "It's only cheating if your partner doesn't know about and accept it."

Once Izuku had their system written down, and hashed out all other potential concerns they could think of, they were pretty satisfied with the final product.