heres my theory, Since hwan was a kid, he wanted chiwoo to be beside him right? So while he was crying because chiwoo left, he saw moony and moony asked why he was crying and said something like if he stopped crying he'll Grant one of his wish but he'll be moony's contracter which is kinda doing something bad. So hwan's wish was to "Kill chiwoo's parents so chiwoo would be next to me forever". And that happened, somehow he knew that his mom would take chiwoo in and they'd be like brothers.
Thats just my theory tho. ╮( ̄▽ ̄)╭







Go queen!!! Purrrrrr