I know the oneshot was really confusing. Okay, there's not much to explain, but I'll try my best ^^

First. Why Yoona hates Luhan. — Yoona is an orphan. She's not the typical or anything, and she was abused by her step-father when she was young. I don't know if I written that or not, maybe I deleted it, never mind. Anyway, in the end her mother died in jail for murdering her step-father. So Yoona basically doesn't trust life or anyone. Until she met Luhan, who's like the exact opposite of her. Luhan is rich, he's exactly like a prince, not very pampered, but never suffered. Luhan met Yoona first in an orphanage where he was helping his father's friend to adopt Yoona. And specifically Yoona because she unfortunately happens to have the same very rare blood type as the sickly rich daughter. I think there's some hint, Yoona was forcefully strapped to the surgery bed so that they could extract her blood and bone narrow. Before that, she was cold to Luhan. And Luhan was cold to her. But she realizes Luhan actually cares for her, except he doesn't know how to show. They slowly got closer and easy to say, Yoona has all the reasons to fall head over heels in love with the caring Luhan. But when Luhan wasn't there to help her out of the surgery table, she felt that she was betrayed. She felt that all the kindness Luhan gave her was pity and nothing else. What she doesn't know is that Luhan had tried to help her, but he was confined to his own room with a broken leg after trying to jump out of his window, which happens to be on the second floor. She doesn't know, Luhan doesn't explain, she hates life, and Luhan.

As to what's the connection between Kris and Yoona. — The only connection is that they both of same painful childhoods, and most of all, their enemy is the same person. Kris' father was killed in a fire by the sickly rich daughter's father, who forced Yoona to go through so many pain. Kris understands Yoona, maybe more that Luhan, is because they somehow shares the same fate. Kris takes care of her, although not very well since he's like a total devil himself. He makes sure she's fine, but at the same time, he has little tricks up his sleeves to test Yoona's feelings.

What's the connection between Kris and Luhan. — They knew each other previously, and they can't really be considered friends because Kris doesn't need friends. And most of all, since Luhan's father is friends with the sickly daughter's father, Kris all the more would not accept him as a total friend. But they have some kind of deal or something. They make use of each other, they take advantages out of situations. Basically, they're alike in some ways and maybe that's why they are able to maintain that not-exactly-friendship-friendship.

Mystery about Kris. — He's my favorite character actually. He has like the biggest mystery of all three in the oneshot. Kris father is killed by the sickly daughter's father because of one will. One will made by his mother, who was the daughter's mother, making her the man's wife. However, she only married that man because of some family deal and her real love is Kris' father. She had left all her money and everything to Kris, which the man was furious with, as he wants all the money and power to himself. Initially, he wanted to kill both Kris and his father, but Kris escaped with the reason shown in the oneshot (I think it was shown...). He basically wants revenge. But I felt like it's a side story so I didn't really add in. His character in the chinese novel is also my favorite because in the end he died for the character of Yoona. And in the novel, he had always been in love with Yoona, however, she doesn't remember him anymore because they part at the age of seven/eight. Maybe I'll write a oneshot about his story, maybe not.

Hm... I think that's all to what I have to say. If there's anything else that is hard to understand, I'll add in or maybe reply on your wall. Thanks ^^