Almost, just use the Sex Note a little.

"Come on, let's go find you a room, then you can get some sleep," Kazuma invited, taking Xylixia's hand.

She blinked, as if confused, probably having expected him to expect her to sleep in his bed tonight. She seemed slightly disappointed. Still, she walked with him as he found an empty bedroom for her. "Thank you for your hospitality," she smiled at him.

"You're quite welcome," he replied, before heading back to his own room and taking out the Sex Note. He considered for a moment about what to do with it, but decided against directly controlling Xylixia for now. She had already proven very submissive, so it might be fun to see what he could get her to do without resorting to use the Note on her.

Well, not entirely... He would still need to make sure she had no issues with the Note, or his harem. So he wrote, "Xylixia will not have an issue with the Sex Note, nor of Kazuma Sato's use of it. Furthermore, she won't be bothered by the fact he has a harem, and will respond to any of his advances as she would normally without it, unless she is bisexual and turned on by the idea of said harem, in which case, she will respond as normal completely. She also won't tell anyone about the Sex Note that doesn't already know."

There. No direct seduction of her with the Note, but making sure his bases were covered. "Let's see how this goes," he smirked, before closing the book and heading into bed.

...

"HELL NO!!!" Aqua shouted over breakfast, Kazuma sitting next to Xylixia.

"I already told you, it's a done deal," Kazuma shrugged as Xylixia ate greedily. "Suck it up."

"You're letting a devil join us!? No, I won't accept it!"

"Fine, go to Kyouya then," Kazuma replied, digging his pinkie in his ear. "I'm sure he's in the market for new party members."

"Ghrrrk!" Aqua growled.

"Besides, it'll be a good learning experience for you to get to know someone you're prejudiced against," Kazuma leaned back in his chair. "It oughta be good for you."

"Fine, but if she puts one toe out of line, she's toast!" Aqua huffed, crossing her arms and turning away.