Abandon Shipping: After Word of God confirmed Sangwoo never had genuine feelings for Bum, several fans ditched the ship.
Awesome Art: Even people who do not enjoy the manhwa's story agree that the art style is distinctive with well-rendered panels, especially as the art evolves.
Broken Base: What Sangwoo deserves for being a sociopathic serial killer, rapist and domestic abuser is a point of debate among many fans. Some want him to get a lifelong sentence in jail. Some want him to die, with or without death penalty. Some want him to get therapy so he can be in a happy consensual relationship with Bum instead of abusing him, despite the fact that he's homophobic, verbally abused Bum in several ways just like Bum's Uncle did (both beat and raped Bum), and Word of God confirmed that Sangwoo is hetero and only saw Bum as a replacement for his mom.
Draco in Leather Pants: Sangwoo, a serial killer who imprisons, tortures, rapes, and kills people, has fans and apologists just because of his looks. It certainly doesn't hurt his image to be drawn handsomely and having a tendency to go around his house shirtless. In the latter part of the story, his troubling backstory (he was emotionally abused by his mother, who also made him kill her) was incorporated into this treatment.
The underage male prostitute that appeared in Chapter 23 and hit on Seungbae got a surprising amount of interest from the fandom and it even got him a modest, yet still solid amount of Fanart, despite of having a very minor role and not even having been named. Borders on One-Scene Wonder.
Min Jieun, mainly for her beautiful physical appearance and some people sympathizing with her.
Friendly Fandoms: Yuri!!! on Ice, despite the fandom rivalry, has quite a bit of fan overlap between the two possibly because of them being complete 180s of each other.
Memetic Mutation: Shipping Yoon Bum x therapy/freedom and Sangwoo x prison/death sentence as Ship Mates.
Mind Game Ship: Outside of the physical and sexual abuse, Sangwoo is also skillful at psychologically manipulating Bum.
Misaimed Fandom: Genre-wise, it's intended to be a psychological thriller/horror story. Despite Yoon Bum being in an abusive relationship with the murderous rapist Oh Sangwoo, many people unfortunately ship them anyway and root for the latter as if it's a romance, just another yaoi pairing, or a kinky dynamic. This is despite the fact that the author stated that they never wanted people to look at the story as a romance.
Sangwoo has already crossed the line since the beginning of the story, having kidnapped, tortured, raped, and murdered many innocent people for years, and he was never kind to Bum to begin with (or to any of his mountain of victims which he had killed by this point) since he frequently beat, tortured and manipulated Bum, but what made him full on cross the line in his "relationship" with Bum is when he beat up and raped him at the end of Season 2 despite Bum having saved his ass at the police station. Another cross the line moment between them is when he beat Bum black and blue near the end of the story, telling Bum how he doesn't need him anymore, and then attempted stab Bum to death when he refused to kill Seungbae. There are several of such Moral Event Horizon moments between them during the story due to Sangwoo's vile actions where he tortures and beats Bum within an inch of his life.
It's already been implied early in the story that Bum's Uncle raped Bum aside from beating and starving him, but when it happend, it felt like a full on punch to the face after Bum's Grandma told Bum how his Uncle went through a lot as a child and how he should try to understand him. Bum was left traumatized the next day, beginning to self harm, running away from home, and hiding in the sauna for a night in fear of his uncle, but as he went home, his grandma threw him under the bus, lying to Bum that his Uncle wouldn't come home that night so that he should sleep in his Uncle's room, causing Bum to get raped by his uncle again after he came home and locked the door and severely beat Bum up with a belt. This went on for years and Bum's Uncle hasn't changed at all when Bum met him again in the present.
Eunseo was never the best parent to begin with, but what really made her cross the line was when she tried to rape and kill Sangwoo. Then she forced Sangwoo to kill her afterwards, saying to him that she hopes he dies a horrible death.
No Yay: Considering that Sangwoo is a homophobic man who abuses, tortures and rapes the bisexual Bum, many people ship them regardless...
Overshadowed by Controversy: It's nearly impossible to talk about this manhwa outside of the fandom without bringing up the controversy surrounding its violent themes and the abusive relationship between the two main characters. Many people outright ban it from certain communities.
Ron the Death Eater: Min Jieun may be a bully, nonetheless, she gets vilified a lot by shippers for "interfering" with Sangwoo and Bum's abusive "relationship".
Signature Scene: From all the way in Chapter 1, we have the scene where Sangwoo surprise attacks Bum with a bat, his face partially in shadow. It sets the tone for the rest of the series on, and the image in particular has become popular in its own right.
Too Bleak, Stopped Caring: With a serious amount of Squick, abuse, killing and many unsympathetic people, it's clear the story won't end on a happy note.
The Woobie: Bum is a orphan who lost his parents when he was very young and was then given to his grandparents and Uncle. His grandpa was seemingly already dead by the time the flashback was shown. His grandmother emotionally abused him. Bum's Uncle gave him the worst time, as Bum was physically, sexually and emotionally abused by him for years because he's the kid of Bum's mother, who left the Uncle for Bum's father. Bum had no friends and was bullied in school. He then was barely cleared for compulsory military service despite being underweight, which lead to sexual abuse from his superiors. And then he gets captured by Sangwoo, the man he was in love with and had truly believed was a great person, who then proceeds to abuse and torture him physically, sexually and mentally, even bringing Bum's Uncle to Bum and leaving them alone despite knowing what Bum's Uncle did to Bum, letting Bum's Uncle and let him beat up and almost rape Bum again. The poor guy just can't catch a break.
