Some brief explanations

After Suu finished syphoning the water from Kimihito, the two of them along with Papi and Miia turned to look at Ria. "Seriously, who are you!?" He said, pointing at Ria. Cerea and Mero couldn't see her, so, after finding nothing, they both looked along the path of Kimihito's pointing.

Ria, meanwhile, was eventually able to stop her laughter, wiping a tear from her eye. "That was so much fun to watch. Oh, I'm Ria, by the way. An Erokami, and the one who dropped your sex note into this world."

"Wait. Let's figure this out in order." Kimihito says, stopping before things got complicated. "First, you threw this at my head?" He reached in and pulled out the sex note, surprised to find out it was still perfectly dry, like it hadn't been covered in water and Suu.

"Oh, I didn't throw it. Like I said, I dropped it. I don't aim for people, though it does have a habit of hitting people on the way down." She grins, holding back a chuckle as she looks at Papi. "And this time, I got a two for one special!"

Ria dropped the book into this world, watching it fall. As it did so, a blue girl with wings for arms flew beneath the book, bonking off her head. The book fell past her as she looked around as she missed it, before she resumed her flight, right onto Kimihito's forehead

"And that's what happened there." She explained, the others who could hear her looking at Papi. "So... you could see her the whole time?" Miia asks.

"Yup! Saw pretty naked lady a few times while flying before I came here." She said in her usual chipper tone.

"All right, that explains the book..." Kimihito nods, looking pensive. "Second question: Why can't they see you?" He jabbed a thumb at Mero and Cerea.

"Because they haven't touched the Sex note." Ria responded in a matter of fact tone.

"Cerea, Mero, could you come over here?" The two of them approached, leaving the water as kimihito tapped them with the book.

"What was that fo- Who are you, foul invader!?" Cerea shouted, rearihg back slightly in surprise, causing her boobs to go into a bouncing fit. Mero was surprised to, rearing back and accidentally falling back into the pool. Miia slithers over to try and calm Cerea as best she can.

"So for question three: why do this in the first place?" Kimihito asks over Ria's new giggling fit.

"Why does anyone do anything? Boredom!" She says with satisfaction. "But if you want an actual reason, I enjoy watching people have all manner of erotic fun, and it gives me a chance to explore the new world."

"All right. Now for the biggest on my mind right now... Why are you here now?" Kimihito asks.