So I'm guessing that those are probably yakuzas or loan sharks. Guanshan's parents owe them, couldn't comply so they tried to take mo guanshan as collateral but dad came right on time and was able to prevent Mo from being taken, everything went downhill and his dad got killed? Thus, resulting a horrible trauma for Mo. So now it's just him and his mom living in that small apartment. They use to be rich?
Remember when Mo agreed to take the blame for that scandal in exchange for money? Maybe that was his way of trying to help his mother? Because he's blaming himself for what happened during that flashback? Anyway..
So I'm guessing that those are probably yakuzas or loan sharks. Guanshan's parents owe them, couldn't comply so they tried to take mo guanshan as collateral but dad came right on time and was able to prevent Mo from being taken, everything went downhill and his dad got killed? Thus, resulting a horrible trauma for Mo. So now it's just him and his mom living in that small apartment. They use to be rich?