Nope. Bad arc. Bad writing. Nope.
First, it's a cliche. I think that's uncontroversial for me to say. You may be fine with cliches, and that's okay. But it's pretty clearly a cliche.
Second, it does the same kind of thing that the stalker arc did a while ago. Remember when there was that stalker student going after that one girl, Jiwon? It was this [male] character introduced without any depth and purely to be an antagonist so that the male main character, Kiryong, could look cool. In addition to being an overly done cliche, it's just cheap and shallow. Two creepy brosifs find the sick and weak Jae-Kyung, and then they (well, one, at least) try to take advantage of her.
I was actually really hoping it wouldn't go this way because they talked about helping her. I thought the writer was actually going to make them have depth of character instead of being plot devices to show off how Kiryong's physical training is being used to protect Jae-Kyung.
It's cheap, shallow, and a cliche.