Momo, but he swaps regularly.

He lined his cock up behind Momo, and said, "You've been waiting for this so patiently..."

"Oh yes, Master... You gonna reward me?" Momo asked with a smile, shaking her butt again.

"Indeed I will. You've been a good slut," Izuku assured, before pressing his cock into her pussy.

"Oh... Ah, yes!!" Momo gasped in bliss as she felt him slowly slide into her. Ochaco glanced her way and smiled, feeling no envy. Why should she? She knew she'd get a turn, and as long as Master was satisfied with his choice, she was happy. Momo had greatly increased her capacity for that little known emotion of compersion. She then gasped as she felt Izuku's fingers start rubbing her folds.

"Oh... Thank you, Master..." Ochaco cooed as Izuku carefully fingered her, knowing he was new at that. Still, he paid close attention to her to gauge her reactions to each motion as he bottomed out inside Momo, so as to improve his learning curve with it. He remained fully inside Momo for several moments as he did this.

"Master, I'm always ready for you," Momo assured, noting Izuku wasn't moving so as to let her get used to his length in her. Nodding, Izuku pulled his hips back, pulling his cock out until only the tip remained, before thrusting back in. "Ah! That's good, just like that, Master!"

Encouraged, Izuku started to speed up, though this caused his cock to slip out. He quickly lined it back up and pushed back in. He then gave Momo's ass a slap. "Oh!" Momo yelped in glee at the sudden hit that made her ass jiggle, and she turned a grin back towards Izuku. "Oh, do that again, please!" Izuku obliged, hitting her other ass cheek. "Yes!"

He continued to fuck Momo for a minute, slipping out another time. However, instead of reinserting into her, he decided to shift to get behind Ochaco, who was pleasantly surprised at his swap, and shifted to raise her hips a bit. He slid himself into her, getting all the way inside her a little quicker than with Momo. "Mmhn!" Ochaco whimpered happily, and Izuku started to fuck her.

Momo turned to gaze at Ochaco, a sultry smile on her face, pleased by this development, not even mad that Izuku had swapped to her. Especially since Izuku had replaced his cock with his fingers in Momo. "Oh, this is hot, Master..." she purred.

"Can you spank me too, Master?" Ochaco asked through her moans, before giving a delighted yelp as Izuku didn't even hesitate to oblige. "Yeah, like that, more!" she begged. Smack! "Ah!" she gasped, beaming as she closed her eyes to focus on the sensations.

Izuku kept going in Ochaco until he pulled out too much again, and swapped back to Momo, fingering Ochaco again. "Enjoying yourself, Master?" Momo asked through her whimpers of delight as Izuku began fucking her even faster, though getting better at being careful not to pull back too far.

"Yeah, I am," Izuku grunted, making both Momo and Ochaco smile even more. As good as it felt to be fucked, their priority remained Izuku's pleasure. Again, Izuku ended up falling out of Momo, and proceeded to incorporate that mistake into switching to Ochaco again. Momo grinned, noticing that pattern, and mildly impressed that Izuku had incorporated minor mistakes brought about by his inexperience into his system of fucking.