Oh, Dear. It would seem MC found where Sissy hid his "special box". But what's in this box, Make up and fur conditioner, and perfume. A shower and a few minutes later, it's good bye MC and hello Mina Cinclaire. Sissy LOVES her sister like nothing else, but she can be such a show off- and that's HER job. Mina knows this, and simply enjoys teasing her. Every so often, Sissy needs to be reminded who's the oldest. :P Unfortunately she can be quite shy when showing off her new look in public. This, and the reason for the MC personality, stems from her past romantic experiences. The most notable of which, is exactly why Sissy knows something Mina doesn't- her conditioner is laced with pheromones. o.0
What we see here is Mina admiring her reflection, and enjoying her sister's jealousy. Sissy's just used to being the cute one, and isn't used to having her sibling usurp her from that title.