the younger sister is showing her true colors.

Though it's very engaging in places, this drama seems like a new genre at times-- a dystopian fantasy in which most of the main characters don't have the slightest bit of emotional intelligence. Eun Jo, even after spending years with people who treat her well, and after she's grasped the unconditional live of her father, and allowed herself to be affected by it, STILL hasn't managed to observe the ways in which even run-of-the-mill ordinary people at least go through the motions of empathy and courtesy, and still hasn't grasped that these superficial niceties are better than her silled-ignorance variety of cruelty toward those who try to get close to her or lean on her for momentary comfort. Hyo Seon hasn't grown up, but there is one realistic aspect to her character-- those emo chicks can become raging, vindictive, succubi when they feel betrayed. Ki Hoon stands around a lot brooding when he should be saying something, but at least he manages to spit out his desires for Eun Jo (fat lot of good it does him, though), and expresses some love for his father in the hospital. Kang Sook the mother is portrayed as such a sociopath through the first 13 episodes that her being touched by her husband's journals doesn't quite ring true-- someone that cynical would have dismissed him as a weak-minded, glutton-for-abuse fool. Ultimately there's no proof adequate to distrust, that is, a truly distrustful person will interpret the most sincere affection as driven by ulterior motives and just extraordinarily well-played fakery, and her distrust will only deepen in the face of such "artful manipulation" or "lap-dog foolhardiness." Fortunately, cynics and socipaoths like this are rare, but the episode 1-13 presentation of Kang Sook seems too extreme to be consistent with her later conversion.
--- Also, there's a lot of pledges to "kill you" or never to leave or always/never to do this or that, which seem not to be taken very seriously. Forget honoring vows or commitments, merely on the level of saving face, there are too many things said that are stated with great import that are just empty words. The exceptions here is Eun Jo's former little stepbrother (can't remember his name), and of course, her adoptive father. In a broader sense, any kind of important behavior pattern that one commits oneself to that causes others harm, requires some kind of humiliation, apology, and a massive questioning of assumptions to change, And there are too many characters that are too committed to being too messed up through the early episodes for their mass redemptions to be believable.