Kdrama S Line Plot Summary Ending Review & Cast [2025]

The Wavve original drama “kdrama s line” is a six-episode fantasy thriller released on July 11, 2025, based on the webtoon of the same name by author Kkomabi. The show is structured around the unique concept of the “S Line,” a red string that can only be seen by a rare few through special glasses or devices. This S Line connects the heads of those who have had sexual relations, functioning as a device that visually exposes hidden pasts, societal hypocrisy, and taboos.

The protagonist, Shin Hyunheup (played by Arin), has the congenital ability to see S Lines and has lived as a recluse after enduring a family tragedy caused by this power. She ultimately resolves to face the world again. Detective Han Jiuk (Lee Soo-hyuk) struggles to uncover the secrets behind the S Lines and a series of connected incidents. Many diverse characters become intricately entwined, including high school student Kang Seon-a (Lee Eun-saem) and teacher Gyujin (Lee Da-hee).

The drama deeply explores the nature of truth, human psychology, and moral confusion, combining thriller and mystery elements. With its unpredictable plot developments, unique characters, and stylish direction, the show created a powerful stir immediately after its release. It received high praise both domestically and internationally, including an official invitation and music award at the 2025 Cannes International Series Festival.

korean drama s line

Title: S Line | Korean S 라인 | Japaness sライン
where to watch : Wavve (Wavve Original)
Genre: Fantasy, Thriller
Release Dates: July 11, 2025 – July 25, 2025 (6 episodes, currently airing/released)
Production Company: Sidus
Filming Period: September 11 – November 27, 2023 (pre-produced)
Original Work: S Line by Kkomabi (Naver Webtoon)
Director: Ahn Jooyoung
Writers: Ahn Jooyoung, Hwang Hogil
Main Cast: Lee Soo-hyuk, Lee Da-hee, Arin, Lee Eun-saem, and others
Viewer Rating: Restricted to mature audiences

kdrama s line plot summary ending review & cast [2025]

KDrama S Line Cast

Han Ji-wook (Actor: Lee Soo-hyuk)
Detective (Lieutenant) of the Violent Crimes Unit 2 at Bangju Police Station. Owner of S-Line glasses (Number 6). A charming, free-spirited womanizer. He pursues the truth of the S-Line and, as Seon-ah’s uncle, seeks to protect her. While investigating a murder case, he approaches the secret related to the S-Line.

Lee Soo-hyuk instagram

Lee Kyu-jin (Actor: Lee Da-hee)
Ethics teacher at Bangju High School and homeroom teacher of Hyun-heup and Seon-ah’s class. A character without an S-Line, she displays suspicious behavior contrary to her appearance. She exudes a mysterious presence, such as recommending students wear glasses.

Lee Da-hee instagram

Shin Hyun-heup (Actor: Arin / Young actor: Kim Ro-a)
A high school student who could see the S-Line since birth. This ability led to tragic family events, and after a long period of seclusion, he returns to school due to an incident. He becomes classmates with Seon-ah and gets involved in various cases.

Arin instagram

Kang Seon-ah (Actor: Lee Eun-saem)
Bangju High School female student, owner of S-Line glasses (Number 2). Ji-wook’s niece and Hyun-heup’s long-time friend. Once a victim of school violence, she undergoes change thanks to the glasses and encounters a new phase. Ensnared in a case, she falls from a rooftop and is left in critical condition.

Lee Eun-saem instagram

Other S-Line Characters

Hyun-heup’s Mother (Jang Sun):
Discovers her husband’s affair through Hyun-heup’s drawing and later kills him and flees.
Oh Jung-min (Lee Ga-seop):
Owner of S-Line glasses (Number 1). Former Bangju High math teacher and has a record of dating violence and murder.
Lee Hee-won (Park Ye-ni):
Neighbor who moved in front of Hyun-heup’s house. Threatened by Oh Jung-min but saved by Hyun-heup.
Han Ho-san (Hong Seok-bin):
Ji-wook’s father. He is in a nursing home; there is lingering resentment between father and son.
Oh Dong-shik (Kim Dong-young):
Detective in Violent Crimes Unit 2. Colleague and partner of Ji-wook, involved in major cases.
Kang Su-min (Seong Ryeong):
Detective in Violent Crimes Unit 2.
Kim Hye-young (Nam Gyu-hee):
Owner of S-Line glasses (Number 3). A school bully who tormented Seon-ah and is in an affair with a teacher. Disappears after stealing the glasses.
Choi I-seul (Kim So-young):
Tormented Seon-ah alongside Hye-young. Takes a bystander’s stance due to family issues.
Yoo Joon-seon (Lee Kwang-hee):
Friend who has a crush on Hyun-heup.
Lee Kyung-jin (Oh Woo-ri):
Hyun-heup’s friend, actively involved in investigating incidents.
Yoon Ji-na (Lee Han-joo):
Idol trainee and class president of the class next to Hyun-heup’s.
Bang Sung-jin (Park Sung-il):
Korean language teacher. Had an affair with Hye-young and, after hurting Seon-ah, took his own life.
Kim Jung-woo (Woo Ji-hyun):
English teacher, owner of S-Line glasses (Number 4). Gets caught up in family-related conflicts.
Music Teacher (Kim Jung-woo):
Has a relationship with Lisa and is killed by Mi-seong.
Kim Mi-seong (Jeong Mi-hyeong):
Administrative staff, owner of S-Line glasses (Number 5). Makes an extreme psychological choice.
Kim Kyung-mi (Lee Sang-hee):
Jung-woo’s older sister, wife of Byung-chul.
Gwak Chae-rin (Oh Ah-yeon):
Byung-chul’s mistress, depicted as pregnant.
Lisa (Bae So-young):
Supposed celebrity. Had a relationship with the music teacher, later threatened by Mi-seong.

kdrama s line plot summary

Episodes 1–2

In the deep of night, Hyeon-heup is tormented by the alienation of being able to see a red “line”—the S-Line—that others cannot. As a child, his ability to see this line led to his mother’s illness and, ultimately, his father’s death. After his father’s passing and his mother’s disappearance, Hyeon-heup recognizes himself as a cursed child and loses even the will to live. After several failed suicide attempts, he finally resolves, “At the very least, I need to find out why this line exists.”

A few days earlier, a woman who stayed briefly in the building next door leaves a peach in front of Hyeon-heup’s house before departing. At that time, Detective Ji-wook spends personal time with a colleague, debating whether to attend a wedding, but soon a young woman is found dead. The crime scene is staged like a theater set—money untouched, the scene unlike any typical crime. Ji-wook is told by a neighbor that a “man in a helmet” was seen entering the villa. A restaurant delivery man becomes a prime suspect, but his delivery records are unclear and those connected to the victim insist their relationship had ended a year earlier.

Hyeon-heup eats the peach left by the woman and debates whether he should report what he’s witnessed. The TV news reports that the main suspect is a delivery man with only one S-Line. While people with hundreds of S-Lines are uncommon, finding someone with just one is actually easier.

The helmeted delivery man soon enters the victim’s home. Hyeon-heup, now a witness to murder, calls 112. The person who answers turns out to be the victim’s boyfriend. At the same time, Hyeon-heup’s niece, Seona, watches the entire sequence of events expressionlessly. At school, Seona is bullied by delinquents and pesters her uncle for money.

The next day, detectives investigate Hyeon-heup’s building and neighboring areas. They notice the suspicious neighbor Oh Jeong-min’s connection with other serial murder victims and pursue him. Oh Jeong-min’s home shows abnormal signs, and when a detective enters, Oh Jeong-min quickly overpowers both the officer and his partner. Wearing a helmet and glasses, Oh Jeong-min heads to his final victim’s house.

Driven by instinct, Hyeon-heup runs outside to save the woman in the neighboring building. At the door, with Oh Jeong-min wielding a utility knife and the victim opening the door, the two confront each other. After confirming the S-Line above the victim’s head, Oh Jeong-min claims, “This is the way for all of us to be saved,” and stabs her. Hyeon-heup, tangled in the confusion, and Detective Ji-wook, both witness the incident and are plunged into chaos. Time passes and Hyeon-heup senses there is another person who can see the S-Line like himself.

An anonymous message reaches Hyeon-heup: “I can tell you the secret of this line.” Hyeon-heup returns to school after a long absence, and meanwhile, Seona endures continued ridicule and violence, her experience contrasted with a note from someone confessing a long-term affection. The homeroom teacher fails to protect her adequately.

One day, a peculiar pair of glasses appears in Seona’s locker. When she puts them on, she’s shocked to see S-Lines above everyone’s head—the tangled connections and secrets of human relationships laid bare.

With the power of the glasses, Seona observes all the S-Lines of those who tormented her, as well as their targets. Secret connections among teachers, bullies, and everyone in the classroom are exposed. Once a victim, Seona begins turning the tables, using her newfound knowledge for both revenge and to gather information.

Meanwhile, Detective Ji-wook investigates Oh Jeong-min’s past and the secret behind the glasses, confirming with witnesses whether Oh ever wore glasses. The stories of Hyeon-heup, Seona, and Oh Jeong-min begin to intertwine around the glasses.

Seona grows stronger, stands up to her bullies, and gets into conflicts. Meanwhile, Hae-hyung steals Seona’s glasses for his own purpose. As Seona tries to recover them—amid threats, violence, and new turmoil—a power struggle over the S-Line secret erupts.

Hyeon-heup starts to believe the glasses could be capable of saving lives. However, as he tries to return to society and confronts the S-Line’s true nature, he faces another crisis.

By the end of episode 2, school violence, illicit teacher-student relationships, malicious uses of the S-Line, the fierce power structures within institutions, and the tragic truth about human relationships are starkly presented. All characters clash over the S-Line and the glasses, as another incident approaches without warning.

Episodes 3–4

In the gray dawn, Detective Ji-wook sits in a patrol car, sleep-deprived, unraveling clues from Kang Seona’s rooftop fall. Hyeon-heup remembers how, after Seona began wearing the glasses, she broke free from bullying and even intimidated others.

At school, teachers and students gather around an unconscious Seona on a round table, burning candles and wishing for her recovery. Some sob, others cast nervous glances out of guilt for their role in her bullying, and friends in the hallway subtly blame each other.

In the hospital, the principal and college counselor react nervously, worried about the school’s image. One teacher yells, “If she wanted to die, why’d she jump at school?” angering Seona’s guardian. In the lobby, students and parents trade rumors over SNS, insisting “Seona was pushed.”

A flashback shows CCTV capturing Hae-hyung stealing something from Seona’s locker. The field trip teacher tips detectives off that “that kid was always suspicious.” Korean language teacher Bang Sung-jin finds unfamiliar glasses on his desk after distancing himself from students for years. After some hesitation, he puts on the glasses.

When wearing them, he sees the red S-Lines entwined above colleagues’ and students’ heads. At first he dismisses it as a hallucination, but after seeing notes in lockers and encountering Hae-hyung again, his anxiety grows. He confides in fellow English teacher Jeong-woo about feeling mentally unstable. Later, Sung-jin, exhausted and confused, waits on the roof, takes off the glasses, and messages, “It’s all over now, I hope I’m set free.”

Late at night, Ji-wook confronts Hae-hyung. Hae-hyung claims, “Seona approached me first; suddenly, the bullied kid came on strong. I felt nothing.” He describes what happened on the roof, at the photo studio, and at the gathering that day—claiming that as soon as he took something from Seona, she changed and jumped from the roof.

The next day, school bully ringleader Kim Hye-young, who bullied Seona, goes missing. Anonymous notes and bloody graffiti appear throughout: “Who killed the Korean teacher?” “Did Kang Seona really jump?” etc.

At the police station, the autopsy report on Bang Sung-jin’s death arrives. His body was found cold in a car in the parking lot, but the line between murder and suicide is murky. Detective Ji-wook reviews CCTV and traces Sung-jin’s last known contacts, the abandoned car, time of death, and staff movements around the incident.

At the same time, Hyeon-heup searches for the missing glasses in Seona’s hospital room. He questions her about their route to the school and who possessed them, but Seona silently weeps without answering.

English teacher Jeong-woo returns to the classroom and puts on the glasses, instantly seeing the S-Lines above everyone—especially learning the music teacher he liked was involved with his girlfriend. Jeong-woo exclaims, “With one pair of glasses, I can see the whole world,” falling into despair and rage.

Anxiety spreads throughout the school. Parents protest in the principal’s office about ineffective student management, while SNS is flooded with hate comments such as, “If you’re the culprit, you’d want to die.”

Cross-checking CCTV, Ji-wook confirms Hae-hyung stealing Seona’s glasses and tracks events on the night in question: the rooftop fight, Hae-hyung fleeing, and Seona’s fall. Ji-wook grows increasingly sure Hae-hyung is the culprit and tracks him closely.

At Bang Sung-jin’s funeral, colleagues, students, and family grieve in a mix of sorrow and emptiness. Jeong-woo, after learning of his sister’s affair and her pregnancy, is left in confusion and anger. Consumed by rage, he follows his brother-in-law to a hotel that night.

Elsewhere, school staff member Mi-seong secretly spies on the private life of the music teacher she admires through the glasses, only to discover he’s involved with a famous actress. Shocked and jealous, Mi-seong begins to blur the lines between reality and illusion under the influence of the glasses. Her growing desire intensifies the misfortune and destruction that spreads to others, putting herself in danger.

Jeong-woo returns from the funeral, dons the glasses, and witnesses his brother-in-law’s affair firsthand. He confronts his brother-in-law at the hotel, struggles to control his anger, and warns, “This is your last chance.”

Meanwhile, among the staff, rumors swirl about the mysterious power of the glasses and the secret of the S-Line, each vying for possession. Mi-seong reveals her inferiority, jealousy, and desires while leading a double life between school and motel.

At the end of the episodes, both Hyeon-heup and Ji-wook recognize a pattern in deaths and disappearances related to those with the glasses and the S-Line. The desire to possess the glasses and their veiled power gradually surfaces, casting a sinister shadow over every relationship—and heralding the beginning of greater catastrophe within and outside the school.

S-Line Drama Ending (Episodes 5–6)

Coming soon ~

Korean Drama S-Line Review

kdrama S-Line drama introduced the setting that the S-Line cannot be seen unless you wear special glasses or devices, emphasizing even more tension and elements of mystery than the original work. Visually, the red line is realistically depicted in the media, and unease and a gloomy atmosphere are maximized using lighting, music, and camerawork. As a result, viewers were able to go beyond mere fantasy and take a deeper look into the reality where hidden secrets intersect, as well as the hidden sides of human psychology.

“S-Line” exposes human hypocrisy, desire, and ethical confusion, and fundamentally raises questions about the boundaries between good and evil, victim and perpetrator, individual and group. Although opinions were divided because it directly addressed social taboos and uncomfortable truths of reality, it showed new genre attempts, originality of the subject matter, and a high level of directing completion. It also achieved external success such as the official invitation to the 2025 Cannes International Series Festival and winning a music award.

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