
He's not forgotten, don't worry. You will know everything, if the artist follows the novel. If you want to know...
SPOILER
It's the shadow we see with the emperor. The one who killed her was a stalker who was obsessed with her, he killed her and then himself and was reincarnated in...DUN DUN... her eldest brother. He's faking his sweetness and is a manipulating ass who's trying to divide Suhee and Jisu

Daaaaaamn.... That would be a good twist. I wouldn't be able to see that coming. She definitely should do that and give him his own chapters to show his obsession behind the scenes. If done well that would save this manwha from the crappy school plot! ヾ(☆▽☆)
It's sad but she's in school and she learned nothing from the experience. Time to drop out and save your daddy some coin. (⌒▽⌒)

Honestly tho. It was amazing till they school arc, but now It's just a crappy circle of nothing happening. I mean, fluff It's okay but it seems that all the interesting plot went down the sink.
The novel is so much better and the part where the bro turned out to be evil almost gave me the chills Σ(っ°Д °;)っ
Hey, who killed the original sanghee? Didn't we forget about him?
We can see that he murderd her, that they knew each other, that he 'loved' her.
Well than, isnt he that emperors shadow guy than? That looks like an option.