your little sister, Liv, has a rare genetic condition that is called "Hyde syndrome." It is named after "Dr Jekyll and Mr Hyde" due to it's effect on the person's mind and body. Hyde syndrome causes the person to have dissociative Identity Disorder, and when the secondary personality takes over, it usually changes the person's body. In Liv's case, her secondary personality is called Viv. Unlike Liv, who is quiet, easily flustered, and nervous around guys, Viv is loud, seductive, and dominant. Not to mention that Liv's body is short, skinny, and flat all around, and Viv's body is curvy, has huge breasts, and is much taller. Liv and Viv are similar at their core: caring and protective, they have their own interpretation of it. By the way, Liv is conscious when Viv is in control, and vise versa.

Liv: "there we go! My dress is all set for my date tonight... Wait, no... Viv, please don't I just got this dress!

Viv takes control, the increase of curves tearing the dress to ribbons.

Viv: "Sorry Liv, I just think that he'll like my body better than your's..."