- Yu Jung is the only son of a wealthy family. His family runs Z Enterprise.
- At the start of the webtoon, Yu Jung is portrayed as someone who is popular, well-off, and gets along with everyone, thus the tag "Mr. Perfect". However, Seol noticed that he has another personality, far from what everyone thought.
- Although he is depicted as someone who helps others, he doesn't like people who leech on him. He shows no empathy or mercy when you mess with him.
- His evident trait is that he bears a kind of "malice" to everyone he hates. He carefully plans out how to get back at them without getting his own hands dirty.
- Jung's attitude towards Seol changes when he gets to know her, and he sees that she is better than he thought she would be. He is sweet and caring towards her. He is also very protective, as shown when he told Seol to stay away from Inho. This split personality makes Jung very unpredictable. Seol says she that sometimes she cannot read what's on his mind, making her frustrated and sometimes scared of him.
- Despite his general mature disposition, he displays childlike tendencies . He also tends to pout and act cute in front of Seol.
"Damn he's a handsome man." - Hong Seol (S3C57)
- Yu Jung is considered handsome as noted by his college classmates. He attracts attention due to his looks and charm,
His style in clothes usually consists of classic menswear pieces like long coats and button-up dress shirts, but he is also known to wear more casual attire. One of his peers points out that he always wears a different watch everyday and they're all expensive brands. Seol bought him a watch that she thought suited him. Ever since, he has been wearing the same watch.
- Father: Jung has a strained relationship with his father. Jung's father, the chairman of Z Corp, has always been stricts with him, expecting and molding him to be the "perfect" son. His father thinks he has weird tendencies which he himself had in the past. He tried to diminish these 'tendencies' by bringing in Inho and Inha. But later on in this story it worsens the situation,
- Mother: Often referred to as Mrs. Yu, Jung's mother has never appeared in the main story except for in flashbacks. She seems to love and care for her son, as seen from the interactions they share. She even argued with her husband about him labelling their son as weird and warned about his decision regarding Professor Baek's grandkids She works abroad most of the time, due to which Jung treasures her gifts a lot, like the Bvlgari watch Jung wore most of the time. In an extra from Season 2, it is revealed that she is an international lawyer and a powerful blogger, who enjoys traveling even when she's not in the job. Jung sometimes visits her at the places she travels to.
- Seol Hong: Yu Jung first met Seol in a drinking session after coming back from a school break. He comes in late and Sangcheol introduces them to each other. After accidentally spilling juice on Han Byeol, Seol observes him from her table and notes that "something is off" with him. Sangcheol dares Seol to drink from a leaf and goes by it, leaving a mess. He turns his head away when Seol glances at him, making her think that he's annoyed with her. Later on he spots a drunk Seol picking up a used cigarette outside while he was on a call and labels her 'pathetic' for such behavior. Seol overhears this which starts the hate relationship between Jung and Seol.
- A turning point in their relationship is when he catches her laughing at him in the English Study Group made by Jaewoo. This made him hate her, seeing her mock him under her breath. Throughout the webtoon series, flashbacks show how Jung made Seol's life a hell after that incident.
- Little by little though, Jung sees Seol as "someone like him". He discovers that she is elusive to others, hides her worries and problems, and has a family that expects too much from her. This discovery led him to take notice of her, and after observing he starts slowly falling for her. He also points out from episode Blank that he liked her because she is different from others as she didn't approach him because of her "personal intentions".
- Inho Baek: Inho and Jung are revealed to be childhood friends. Brought in by Jung's father in his attempt to rid Jung of his "weirdness". Although having a contrasting a personality,Jung and Inho became friends. Inho and Jung were close in high school–along with Inha Baek, Inho's sister. The trio would hang out at break, stick up for each other, and sometimes go to each other's events (e.g. Jung would often accompany Inho to his recitals.) However, their relationship fell off after a misunderstanding in high school, where Inho would lose his ability to play the piano impeccably with his left hand and ultimately, his once unfaltering confidence. Inho blamed Jung even though he wasn't invoved and has hated him ever since (which is shown throughout Season 1 and 2.)
- He understands that he and his sister are leeching off of Jung's family, and often rubs this in Jung's face. Additionally, his amiable relationship with Seol often irritates Jung as well. The two fight physically and verbally many times in the comic, the most physical one being after they left Seol's family's restaurant.