@Shizukachan it's not that complicated. I think of it like those games where characters have high/low affinity towards light or dark magic. If a character is good at one, they tend to be weak/incapable of using the other.
I did not remember nor read any part of this antagonist in the 1st volume, its either they shifted the plot from volumes 3 and beyond or non LN canon. Can someone lay spoilers please about volume 2 beyond?
Hope the prince doesn't try to control her after finding out how powerful she is. But it would be nice to see him start ignoring the sister and she gets upset about it
I can't really make out the little sister, I think her name is Christa? If she's a bitch she's being real low-key about it.
On Pg. 18 though it was small, she really cared for Drossel's (Leti) safety.