Title: 7/10
First off I would like to say that your main poster (the one used here) is gorgeous. WOW.
But on to the title! While it is a unique and intriuing title, it is hard to say how well it corresponds with the story because it is not a word I know. Having a title in a language other than the one that the story is written in is difficult, because people might pass over the story because they do not know what it will be about. Your title should be a hint as to what the story will be covering, and when it is in a foreign language, the reader can't know what that might be.
Now, after googling the word, I do agree that it fits the story. However, I stand by what I said about the language barrier. People will pass it over because it is an unknown.

Plot: 27/35

                5/5: Originality
                So far this story is nicely original! I haave read stories of missing princesses and whatnot but none set int a modern world or with such an interesting family dynamic. 

                9/10: Believability
                Most of the story is quite believable, especially how you have set up the relationships with the girls and used those to explain the world around them. However, I have to point out that the poisoning not being caught by doctors is impossible, so why not simply make it a new poison that they have no cure to? Also, Shin Hye not knowing that Ji Won is not truly her little sister is also impossible. According to your character chart, she would have been three or four when Ji Won arrived and Shin Hye would have been old enough to know that her mother was not pregnant. So is she simply keeping that fact away from Ji Won? From the conversation being in her own POV it did not seem that way, but it would make a lot more sense. Also, the album having dust on the cover yet having been disturbed by the break-in, that is also impossible. Making it clean would be better and it still would not raise any suspicion, seeing as it is inside of a box and should not have dust there anyway.
                **Edit: The author pointed out that a few answers will be coming about the first two points and so this score has been changed accordingly.

                10/10: Narration
                I really like your narration style, it's very consistent and smooth (despite the tense changes which I mention later). I especially like how you show glimpses into everyone's POVs, it is refreshing and nicely done. In chapter three, your font abruptly changes to bold, you might want to fix that. =)

                5/10: Setting
                I would like more setting to your story. What does the girl's apartment look like? Do they both have their own rooms? What does Min Ho's car look like? Where is the girl's apartment located, what floor? What kind of neighborhood do they live in? Adding in details of the surroundings will help your story to feel more realistic and come to life for the readers. As it is we barely have any information of the physical world this story is set in.

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