I can't remember which story it was, but there was one where two twin sisters were born instead of the intended one, so instead of on with a lot of power, the power was divided between the two though unequally so one had barely above average and the other one was just weak. The above average dies if I remember correctly so the weak one gets all the power as it was supposed to be all the power in just one person. And she gets better and powerful.
I'm kinda hoping it's not the case her as I would like her brother to be good. Bit maybe it's a similar case?
Spolier
I read the spoiler somewhere. You are correct.
which part?
Where'd you read spoiler
I read in novelupdates forum but maybe im wrong.
It's just my speculation. But what if our FL is actually the one with magic power?
I mean, it's strange that her hair went white whenever she was in pain. It's as if someone is deliberately draining the power from her body. There are times when her brother's words seem strange for various reasons. It's as if he can't live without FL because he'll be rendered useless without her. Also, he suggested that FL could be healthy after his death. And, indeed, she is gradually getting healthier than before. So, is it what I think it is? Maybe the 1st magic circle can reveal the secrets later on.
Perhaps her magical power is restrained or maybe too potent, leaving her spellbound? Or perhaps she is similar to (or actually) one of the dragon's disciples? Her brother also said that Arghan will always exist if she's alive. And there's a hint that the royal family intentionally hide her from the outside world. So, maybe... Just maybe it could be the real reason?
Well... I'm not sure tho, it's just my random thoughts. Can't wait for the next updates ╮(￣▽￣)╭