Make her demonstrate her submission.

"Kneel," Ria ordered Sakura, and she immediately fell to her knees. "Who I am is your Mistress for a bit, you can call me Ria otherwise."

"Yes Mistress," Sakura nodded, looking at Ria with arousal.

"Now crawl over here and worship my feet," Ria added, floating low enough to put her feet within easy reach once Sakura had come over.

Sakura nodded and fell to her hands and crawled on over. Upon reaching Ria, she gently caressed her right foot, and began to kiss it.

Naruto decided to perform a small test and said, "Hey Sakura, stop doing that and come make out with me."

Sakura however glared at him a little and said,"Wait your turn idiot, Mistress Ria has me until she's done or is out of time, whichever comes first." She then started licking the foot, not even questioning what she said about Ria's time.

"Just making sure I wrote it right and that we couldn't infringe on each other's fun," Naruto answered Ria's slightly inquisitive look.

"Good to hear," Ria nodded as Sakura switched feet, sucking on Ria's toes. The next ten minutes progressed with Sakura pampering her Mistress's feet while Ria explained who and what she was, and Naruto's new arrangement with her. Sakura took in the explanation without batting an eye, and was soon told to stand and remove her night robe. She then stood, awaiting further orders.