He ultimately decides to allow it.

"...have you made any other wishes to try to expand the harem without my knowing?" Izuku asked Setsuna intently.

Setsuna paused, and sweat just a little. "Um... Maybe not so much to expand the harem, but... You know how Shiozaki keeps being a little judgemental and holier than thou towards us whenever she sees us?"

"Oh good God, what did you do?" Izuku face palmed.

"Nothing major. I just wished earlier today that she would start having her own vivid dreams, with her own fetishes, without any of her arbitrary societal and religious inhibitions, completely separate from our own dream fun. Nothing that would turn her into a slut, just something that would make her a bit less judgy over time," Setsuna replied, shrugging. "...what? It's annoying."

Izuku sighed. "Very close to the line, Setsuna... No more wishes regarding anyone not currently in the harem," he stated.

"...fine," she pouted, crossing her arms. "I still maintain I did nothing wrong... Maybe a bit mischievous, but nothing outright over the line."

"Yeah, but you came close. As for Melissa... I'm not against her joining the harem, but only after we spend some more time getting to know her," Izuku pinched the bridge of his nose.

The girls all giggled. "Well, that worked out!" Ochaco grinned.

"Don't get too excited yet," Izuku snorted.

"Oh, the chicken is already hatched, you're the one who wants to wait to count it!" Momo stuck her tongue out as they walked back to where Melissa was, and saw her standing with her arms behind her back, shifting from foot to foot.

"...so... You guys talk about it?" Melissa asked carefully.

"We're all open to letting you join our little... Group. But we need to know you a little better first," Izuku told her slowly. "But it's not out of the question."

"Speak for yourself," Momo grumbled quietly, already ready for Melissa to join the harem. She would have been fine with any girl Izuku was attracted to joining, quite frankly. She stuck her tongue out as Izuku gave her a look.

"... that's fair," Melissa smiled a bit, before joining them while walking back to the medical wing. "But... I got a real good feeling about you, Deku..." she told him, and he flushed as they were about to turn a corner.

"I AM HERE!!!" All Might declared, shooting around the corner from the other side, and making everyone yelp in surprise.

"Damm it All/Uncle Might, stop that, you're going to give someone a heart attack!" Izuku and Melissa shouted at once as they tried to get their heart rates under control, before pausing, looking at each other, and flushing as they looked away.

"Ah, sorry, sorry, bad habit," All Might confessed, rubbing the back of his head. "More importantly... Melissa, may I have a word?" he asked her, a bit awkwardly.

"...um, okay, sure," Melissa replied, before following All Might somewhere private, Izuku briefly wondering what that was about, before deciding it wasn't any of their business. They headed towards the medical wing, leaving Melissa and All Might to it.