Lift her skirt, then suck on his fingers.

Deciding to test her submission, he ordered, "Alright Mira, lift up your skirt so I can see your panties."

"Of course Master!" she cooed, ecstatic to get even a simple order like that to follow. She reached down for her skirt, grabbing it and pulling it up. Natsu gazed eagerly at her cute white cotton panties.

"Good girl, keep holding your skirt up until I tell you otherwise," he smirked.

"Whatever you like Master," she said, eye smiling as well as actually smiling. Natsu looked at her panties keenly, before looking back up at her. He then decided to test her further, and held two fingers in front of her face. She blinked, and waited for him to order her to do something else.

"Suck on my fingers," he told her.

"Yes Master!" she ecstatically replied, leaning forward with her mouth open, and closing it over his fingers. Moaning as she bobbed her head on them, she still kept holding her skirt up.

Natsu almost couldn't believe this. Mirajane was completely in his thrall, and even better, she loved it. He could see the bliss on her face even as she sucked on his fingers, just being in his presence and obeying his orders was heaven for her now.