The plan was simple. Ming Tao was still in their hypnosis but was fighting it. That was the reason he barely reacted to Mira's disrespect. In order to break that, Hye Yang needed to let him catch Mira alone with her past lover in a situation that would be inexcusable.
And she had found the best time to do so. Right when Mira was having her bath. She would be naked and that would be when Mu Yang would show up. So close to her and also naked. He would corner Mira and be so close to her that it would look like they snuck out to be promiscuous and that would be the perfect cute to walk in on them with Ming Tao by her side. Just thinking about it made Hye Yang's body excited. Her sister would not know what hit her and with the lion king gone, courtesy of Hye Yang's deception, there would be no one to save Mira from Ming Tao's wrath.
