Younghoon is a psycho cause he's also known as a wanted serial killer cause one day he killed a guy who was his enemy and Younghoon had another target but it was a child... named Lee Kaeyeon a daughter of a mafia boss named Lee Sangyeon cause Younghoon was one of Sangyeon's secret agents and Younghoon was a soft guy then but the reason for wanting to kill Kaeyeon was because Kaeyeon treated him like a maid but Younghoon didn't want to treated like a maid so one midnight... he bring Kaeyeon into a alleyway and killed her and you witnessed it cause you were even a secret agent of Sangyeon cause you were just buying food for Sangyeon and you quickly ran away after seeing it before Younghoon sees you