Ya I've been trying to find clues to lead up to that situation. My guess is that when she was young, she ran to the royal palace or something to see her dad, this is probably how the emperor found out she was his weakness. And before that, he was always away because of the emperor's summons / missions, which also explains how he missed her debut and birthdays and stuff. The parts I haven't figured out yet is why he always seems so cold / strict when he talks to her, and how he hasn't showed his affection in any way period for her. I mean at this point the emperor already knows she's his weakness, so no need to hide it. I can only conclude that he is tsundere. Also I think there more going on with that protection that she doesn't know about that ML mentioned, which might lead to more clues. He does appear to be a man of few words, and the fact that she never knew his disciple was the crown price who also had a god awful reputation for loving torture was just a perfect storm for all of that.
I love the father and all but the fact that he fucking gave her a knife without explaining and sent her to the shadow room is just a no. Like bitch what you want me to do with a knife in that situation?