For those who don't understand, that was the old story when he first got out of prison. He killed the people who bullied his sister, and then he had to go to prison. But the man who got him out wanted him to work for him, so now he has this job and works for this man. He talks about Sejin all the time, and he said he felt guilty for leaving him alone after his mother died. I think that's already the third season, because everything is always explained at the beginning of a season, and that was the explanation of what's happened so far. P.S.: Sorry it's so long.