Yoon Bum is depicted as a scrawny young(middle aged by Sangwoo) man due to being underweight. Having straight short black hair with bangs that part down the middle of his forehead and has black eyes with what appear to be notable bags under his eyes.
Yoon Bum is the protagonist of Killing Stalking. A troubled man with a difficult past, he falls for Oh Sangwoo, a university classmate who served the military with him. Bum's crush transforms into an obsession, leading to him to trespass Sangwoo's house by cracking the pass-code on the door and break in. He is depicted to have engaged in inappropriate behavior to maintain relationships with others, most evident in his past acquaintance with a female classmate enrolled in a college four years late and met Sangwoo in the second semester of his first year of Sungsoo University. Due to it being required for men and maturing boys to serve in the Korean military, Bum received confirmation after his first semester of college, despite his previous presumption his underweight body would exempt him from active duty. He was ostracized in his unit and his direct commander attempted to sexually assault him. He was told later that the attempt was stopped by Sangwoo. When he completed his military service, he saw Sangwoo again with a girl. Although he attempted to deny his feelings of attachment toward him, he was unable to stifle them, remarking them as something he "wouldn't be able to forget as easily as before".