probably because the first time she tried to commit suicide it made him realize how much he should've charished her so when she came around he probably made a mental promise to cherish her thus the way he's acting now...Just a theory
I think the reason he was so distant when she was younger was so the emperor wouldn’t exploit his weakness (her) and so she wouldn’t get hurt. And I think the reason he sent Mikhail to “execute” her was because they had a plan to save her. Anyways that’s my theory (๑•ㅂ•)و✧
*spoiler*
Ppl, duke was an asshole before because like what the other person said, she is his weakness and the emperor will take advantage of it. He gave her a dagger to protect herself, but she misunderstood it and thunk her father is asking her to commit suicide, the crown prince is the discipline of the duke and probably ask to save her and not to kill her, the crown prince is said to have no lingering feeling for any of his family so I think he won't act like that... I just read spoilers before when this manhwa released and yes, Misunderstanding is very strong in this manhwa
Fuck I meant max* I mixed up his name with that scum Mikhail Σ(っ°Д °;)っ
I was confused at first too, but I get anyways
Maximillian
does she ever find out why her father acted the way he did ?