I don't think I got the plot. Does he marry his sister or what?
His sister fell in love and got pregnant with someone who has a girlfriend. So that his sister remains happy, he decides to marry the girlfriend of the guy that got his sister pregnant.
OH NO THAT PREVIEW. This is gonna have a bad ending I fear.They already gave us a lot of Chang Min-Jin Hee moments in the latest episode so I think they're gonna separate them. SOMETHING TRAGIC IS BOUND TO HAPPEN. DAMNIT