I'll be blunt. She's miming a BJ.
— Tatsu the Wicked (@tatsunical) April 29, 2016
Street Fighter 5 video shows background character playing the invisible skin flute
The motion is a part of her animation loop, and she's either trying to throw Nash off his game, show Guile what he's got in store for later if he wins, or has a terrible case of oral fixation that is spilling over into her professional life. She's still in her uniform, after all.
I don't know about you, but seeing a resounding wallop to the rear is nothing compared to a gesture that has no other connotations than that of being lewd. I wouldn't be clutching my pearls over it, but if Capcom were so concerned with censoring content that might make people uncomfortable, how on earth did that get through?
Have you spotted any other weird goings-on with the background characters? Let us know in the comments.