i think Daejun took over the branch Hajin was heading because there was a small panel where his dad asks him(hajin) to take over the finance branch or something.
Daejun doesn't have any weird connections with sihyeon but got curious about him through his interactions with him. Initially he planned on killing him but then he started noticing mannerisms which reminded him of Hajin, so he investigated sihyeons case via the doctor and I think he also started suspecting that hajin was the one in sihyeons body. The main sponsor who traumatized sihyeon in the past hasn't been revealed yet along with his other experiences.
Oh and yea, sihyeon was the one who crashed into daejun and hajins car, i believe it was an accident
Hope that makes more sense.
I need someone to like dumb down the plot to me cause I’m like lowkey confused. Daejun is Hajins assistant (kinda) from his old life right? And so did Daejun inherit the business or whatever because Hajin died? also was Sihyeon the car behind them that caused the crash? And Daejun knows that Sihyeon is actually Hajin and that’s why he likes him right? Not cause he has some weird connections to Sihyeon..?