She accepts, and decides to be a sex .

Ochaco thought hard about it. It felt so surreal, just how aware of herself and her own desires she was. Her sexual side was extremely forthcoming. The idea of being completely submissive to Izuku in bed... That appealed to her immensely. Letting someone else take charge of her turned her on just thinking about it. She was definitely joining the relationship, she was just thinking about what she wanted out of it first. "...I'd like to join," she said with a smile.

"That's great! And in what capacity would you like to be a part of our relationship?" Momo asked, clapping her hands together in gleeful triumph.

"Full sex ****, but only for sex," Ochaco replied. "Outside the bedroom, I want an equal dynamic."

"That's definitely more than reasonable," Izuku nodded, almost not believing just how eagerly Ochaco was going along with it. "...you didn't implant any thoughts in her head, did you Momo?" he asked suspiciously.

"Nope! I couldn't use my magic without your permission, Master! Maybe interpret a wish somewhat, but only if I was certain it was something you'd be okay with," Momo smirked back. "You would be surprised just how many people are sexual submissives by nature. Obviously not everyone, but enough for you to have a pretty easy time finding a willing harem with my magic to help things along~!"

"...alright, then I wish that whenever we're in a sexual situation with Ochaco, she will eagerly obey my commands and feel the same way about it you do, or at least as close to it as she can without actually being a genie like you, but only in such settings. Otherwise, she won't be under any magic, except she can't tell anyone you're a genie without permission."

"Done, Master!" Momo smiled, snapping her fingers, and casting her spell on Ochaco.

"Oh..." Ochaco moaned as she felt Momo's magic overtake her, and produce a pleasant sensation.

"...now... You wanna leave the dream now? Or should we have some fun first?" Momo grinned.