"Y-your booty, my goddess?" Rivalz repeated, slighty shocked but at the same time pleased.
"Yes, my booty. My ass, in other words. I'm sure you can do it!" and she winked after that.
"O-of course I can!"
"That's a good boy." Milly placed Rivalz back on the soap and turned arund, showing her perfect backside to the world... well, to Rivalz. She then picked him and placed him on her back. "Leave no little bit dirty!"
"Yes, my goddess!" Rivalz happily replied as he started rubbing Milly's round, delicious bottom. Her lovely buttchecks jiggled with the rubbing, and Milly moaned. She was loving the washing.

After a few minutes of a pleasant ass-rubbing, Milly asked "Hey, Rivalz, do you like bubbly baths?"
"B-bubbly? Yeah, like everyone else, right?"
"What a good thing to hear!"
"Why's that so, my goddess?"
"Because of this!" and right after saying that, she submerged her butt under the water and left out three farts on a row. FRRRT! PRRRT! BRRRAP! "Now this is a a bath, right?" she said giggling while she lifted her ass again.

Rivalz wasn't exactly in agreeance with Milly, though. These farts had taken him by surprise, and caused him to choke and gag. Fortunately, this WAS a huge bath. after all, so he quickly dropped into the water faking he tripped, the liquid element sending him back to Earth.

"What's wrong, Rivalz? You slid?"
"Y-yeah, sorry my goddess. And this bubbly bath is wonderful."
"Well, isn't great you agree with me! I have another special thing to ask of you..."
"Yes, my goddess?"
"Clean the inside of my anus!"