Kim You-Jung as Baek Ah-Jin in Dear X official poster Image Credit: TVING | Monster Union | Siwoo Company
Dear X is a gripping psychological thriller that dives into the dark world of ambition, manipulation, and trauma.
The series stars Kim Yoo‑Jung as Baek Ah‑Jin, a brilliant but emotionally detached woman, and Kim Young‑Dae as Yoon Jun‑Seo, her loyal childhood friend who becomes entangled in her schemes.
As the drama unfolds, viewers are drawn into Ah‑Jin’s complex psyche, the lasting scars of her childhood, and the morally ambiguous relationships she forms.
One of the central mysteries revolves around who is X in Dear X and why the show is depicted as a letter to the character. Before we unveil that, however, let’s go a bit further to the start of the show.
Table of Contents
- What Happened to Baek Ah‑Jin’s Childhood?
- Why Does Yoon Jun‑Seo Help Ah‑Jin So Much?
- Is Dear X Based on a Webtoon?
- Who Is X in Dear X?
- Frequently Asked Questions
What Happened to Baek Ah‑Jin’s Childhood?
Baek Ah‑Jin’s early years were defined by adversity and abuse. In flashbacks, she is revealed to have endured domestic violence from her drunk mother, who also taught her how to steal liquor from a nearby store.
When her father, Baek Seon-Gyu (played by Bae Soo-Bin) found the opportunity, he carried her to the top of the stairs and pushed her to the street; making it look like an accident. Ah-Jin witnessed the incident and even grew numb as her mother pleaded for her to call an ambulance.
Because of her trauma, Ah-Jin learned how to hide her emotions and to manipulate others to survive. She is labelled as a sociopath at the start of the series.
Her rise to fame is not only a career choice but a survival mechanism — she crafts a flawless public mask to hide the damage beneath. The childhood trauma gives her both a motive and a method: the trauma becomes the lens through which she views relationships and power.
Why Does Yoon Jun‑Seo Help Ah‑Jin So Much?
Yoon Jun‑Seo has been steadily supporting Ah‑Jin since childhood, offering protection and devotion that she rarely allows herself to receive. The two met shortly after Ah-Jin’s mother passed– when Seon-Gyu brought Ah-Jin home to meet his new wife, Hwang Ji-Sun (played by Kim Yu-Mi).
Ji-Sun is Jun-Seo’s mother, the result of an affair with whom he believed was their family driver. Ah-Jin’s cleverness enabled her to discover Ji-Sun’s secret, which she used to prevent Ji-Sun from being sent to an orphanage.
But because of her hatred for Ah-Jin, Ji-Sun tried to drown the little girl in the tub– an event that Jun-Seo witnessed and carried with guilt throughout his life.
This is what has led him to aid Ah-Jin despite her wrongs: a trauma bond that he witnessed after the abuses that Ah‑Jin suffered from Ji-Sun and her own father. As a result, the two carry a toxic connection.
While he isn’t as manipulative or disordered as she is, his loyalty verges on codependency. He encourages her greatness, sometimes at his own cost, and the emotional mess is real — both vintage for thrillers and rich for psychological study.
Is Dear X Based on a Webtoon?
Yes. Dear X is adapted from a popular Naver webtoon by Vanziun. The live‑action version emphasizes darker psychological themes, amplifying Baek Ah‑jin’s emotional detachment and ambition in a more cinematic fashion.
So far, we’re loving this transformation of Kim Yoo-Jung, whom we last saw in Chicken Nugget and My Demon. In particular, her rooftop scene after her father’s death has sent chills down our spine as her very image has changed right before our eyes– truly spectacular acting from Yoo-Jung.
Who Is X in Dear X?
So who is this X that is being referred to in the series?
In the title Dear X, the letter “X” refers to the people Ah‑Jin will target, manipulate or betray — her next victims or stepping stones in her ascent. Promotional material describes how she leaves a trail of broken people behind as she climbs.
In the context of the show, her known “X”s so far include:
Yoon Jun‑Seo
Despite his loyalty to Ah-Jin, he is deeply rooted in guilt for the way she turned out. This is why he feels compelled to help and turn her into a better person.
So far (spoiler alert), she has manipulated him to pretend to be her stalker and even admit to having killed her own father.
Kim Jae‑Oh
Kim Jae-Oh (played by Kim Do-Hoon) is another of Ah-Jin’s Xs. After discovering that he steals things in their classroom, she manipulates him by helping her collect money from other people.
Because they both share the same trauma from an abusive father, Jae-Oh feels like Ah-Jin is the only one who understands and supports him. This is why he stays loyal to her, even in the midst of a class controversy.
Sim Sung‑Hee
Unlike Jun-Seo and Jae-Oh, who are both willing Xs of Ah-Jin, Sim Sung-Hee (played by Kim Yi-Kyeong) is not. She is Ah-Jin’s former classmate who bullied her because she only came second to her despite her family’s influence.
She is the only one who has seen Ah-Jin’s dark side, but she responded by bullying and embarrassing her. In response, Ah-Jin destroyed her by framing her as the class thief.
Choi Jung‑Ho
A retired baseball star, Choi Jung-Ho (played by Kim Ji-Hoon) lives by being the voice of the abused and goes out of his way to protect others. He owns Xanadu Coffee, where Ah-Jin works part-time after seeing him fight against a thief.
Ever since then, Ah-Jin has figured out a way to manipulate Jung-Ho to kill her abusive father for her, framing him as the stalker who has been following Ah-Jin around.
Each “X” is someone she uses either for ambition, protection, or survival — they are both collaborators and casualties of her drive. We’re yet to see who the other Xs Ah-Jin will come across in the show. But other than Sung-Hee, we’re already feeling sorry for her victims, especially Jung-ho and Jun-Seo.
The question isn’t just who she will use next, but whether someone will finally undo the mask she wears. Let’s find out in the next episode.
Frequently Asked Questions
What is Dear X about?
Dear X follows Baek Ah‑Jin (played by Kim You‑Jung), a top actress whose glamorous facade hides a traumatic past and a ruthless drive for power. The series explores her manipulative ascent, the people she uses and hurts along the way, and the cost of hiding behind a mask.
Who stars in Dear X and when did it premiere?
The main cast includes Kim You‑Jung as Ah‑Jin, Kim Young‑Dae as Yoon Jun‑Seo, and Kim Do‑Hoon as Kim Jae‑Oh. The drama premiered on November 6, 2025, on TVING and streams in selected regions on HBO Max and Viki.
Is Dear X based on a webtoon?
Yes — the series is adapted from a Naver webtoon by Vanziun. The live‑action version deepens the psychological and visual intensity of the original.
What kind of character is Baek Ah‑Jin?
Ah‑Jin is depicted as brilliant, charming, and outwardly kind, yet shaped by childhood abuse and trauma. She uses her emotional unreadability and manipulation as tools to advance her career — described in media as “angel‑faced devil.”
Why Is Jun‑Seo Helping Ah‑Jin?
Jun‑Seo has a lifelong bond with Ah‑Jin. He served as her protector and supporter through her past trauma, creating a psychological link often labelled a trauma‑bond: he witnessed her suffering, feels indebted, and becomes codependent with her in his devotion.
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