Pretty sure she was there when they planned the mall trip, she just silently invited herself to it. Probably snuck into the changing room while they were picking out swimsuits. But even without that, we already know she has full control of his phone.
He should have asked for the sock back once she removed the promised "freedom" outside of the shoot
Which one?
At this point his captor is better suited for him. While his new gf may be equally pervy, his captor is willfully indulging him is his fetish desires without being even a tiny bit put off by it. In fact his deviance and her control turns her on. Pretty sure the feeling of stealing her man knowing how much she was into him and that there is nothing either of them can do is ...
She is the biggest pervert of all of them and I'm all for it. MC doesn't mind being stepped on and has been slowly realizing he is all for the S&M play.
We haven't seen the misanga since chapter 13 at the karaoke love talk scene. It must have fallen off. I'm guessing that her wish to be with Atobe is slowly coming true but not in the dreamy romantic way she probably wants.