Yoon Bum is a quiet, shy, timid, and sensitive individual who suffers from borderline personality disorder and often struggles socially.

Dealing with his uncle's abuse, loneliness, and thinking that he is not needed by anyone, Yoon Bum cut his wrists in the past regularly to cope.

Behind his fake facade in public, he is actually a cruel and ruthless individual who kidnaps, abuses, tortures, rapes and kills people, showing absolutely no mercy to his victims or remorse for any of his actions.

He is highly narcissistic and looks down on everyone, pretending that he actually cares for others, only to strike them with honest hostility when he feels like it.

As noted by his superior, he appears to pry too much into investigations and trusts his (usually accurate) intuitions even when lacking evidence.