Kim Rok Soo didn't transmigrate, he died in the attack where he was meant to and reincarnated as one of the orphans in Toltz territory.
With his sticky fingers and predilection for sticking his nose in everyone's business, he actually found out when Venion had a dragon egg, of all things, being wheeled through the territory.
And, naturally, he realized exactly what was meant to happen to that dragon.
So he concocted an elaborate plan and tried to steal the egg, only for it to hatch at the worst possible time and for both of them to get caught.
Kim Rok Soo and the little dragon are chained up and tortured, instead of just the little dragon.
Rok Soo antagonizes Venion to take the heat off of the dragon, and the dragon in turn does the same when it's been too much for Rok Soo.
Then, three years after his capture, the entrance caves in as Choi Jung Soo and Lee Soo Hyuk stand in the rubble, wild eyed and pissed.
They'd been transmigrated, and had only been in the world for seven months.
They'd bullied the God of Death into telling them where Rok Soo was.
Soo Hyuk had straight up punched the God of Death in the face the second the phrase "dungeon" left the god's mouth.
They'd been searching for him the entire time, bullied a counts son for political information, bullied Choi Han into being their interpreter, punched their way through so many guards that if it hadn't been for the count's son's money they definitely would have been on wanted posters, and they'd just found him chained and beaten.
Rok Soo thinks it's fantastic; he gets reunited and also gets to leave.
Soo Hyuk and Jung Soo think...well. Not a lot, really. They saw a tiny Rok Soo beaten to hell and their minds kind of went blank.
By the time they come back to themselves Venion is in pieces. Literally.