Imagine if everyone knew the history of your personal relationships—how embarrassing would that be? That is just what the drama S Line delves into, and it is both fascinating and unsettling. The show takes something extremely private and makes it public, raising serious problems about trust, privacy, and judgment.
If you’ve read our past reviews of shows like Law and the City, you’ll know we enjoy dramas that don’t shy away from messy human emotions. S Line does just that. After just two episodes, it’s already giving us a blend of mystery, fantasy, and a whole lot of complicated feelings, wrapped up in a visually stylish package.
Quick Drama Facts
Drama: S Line (에스라인)
Network / Platform: Wavve
Premiere:11 July 2025
Aired On: Friday
Genres: Fantasy-thriller, Mystery, Coming-of-age
Based on: Webtoon S Line by kkomabi
Cast & Characters
Lee Soo-hyuk as Han Ji-wook:- A sharp and emotionally layered detective. He's calm on the outside, but battling guilt, secrets, and now—supernatural truths. The deeper he digs, the more personal it all becomes.
Arin (Oh My Girl) as Shin Hyun-heup:- A quiet, introverted high school student cursed with the ability to see people's red S Lines even without the glasses. After getting involved in some tragic events at school, her quiet and lonely life starts to change. She’s not just someone watching—she’s the key that connects everything.
Lee Da-hee as Lee Gyu-jin:- She’s a new teacher at Hyun-heup’s school. While everything around her is full of strange events, she stays calm and untouched. She has no red thread, which makes her mysterious. She’s quiet, serious, and might have a link to the special glasses.
Before Starting, Let's Figure Out What “S Lines” are.
In the world of S Line, an S Line is a glowing red thread that appears above two people who’ve had a sexual relationship. These lines are completely invisible to the average person, but not to everyone.
At the start of the series, only Shin Hyun-heup can see these lines naturally. For her, it’s a painful curse. Every time she looks around—at classmates, strangers, even teachers—she sees their private histories floating in the air like glowing red connections.
Later, some other people gain access to this ability through special glasses that reveal the S Lines. And once that happens, things get complicated—fast.
Episode 1 — “Eyes That See Desire”
The first episode begins with Shin Hyun-heup, a quiet girl who carries a strange ability—she can see glowing red lines between people who have had a sexual relationship. These lines are called the “S Line.” No one else can see them, and honestly, it freaks her out.
The S Line has caused her a lot of pain. Because of it, her mother killed her father, and Hyun-heup even tried to take her own life, though she survived. Traumatized, she shut herself away in darkness so she wouldn't have to see the red lines anymore.
One day, Hyun-heup sees someone trying to kill a girl in the building across from hers. Gathering her courage, she runs over to save the girl.
On the other hand, Han Ji-wook isn’t your typical drama detective. From the moment he appears in episode 1, he carries a quiet intensity. He doesn't talk much, but when he does, it's sharp and to the point. Ji-wook has a niece, Kang Seon-ah, who was being bullied at school—something he was completely unaware of.
Ji-wook is smart, observant, and confident. He picks up on things others miss. But here’s what makes him stand out—he's covered in red S Lines. When Shin Hyun-heup sees him for the first time, she’s overwhelmed by the sheer number of threads around him. This guy has a past. A complicated one. And that makes him instantly mysterious.
Ji-wook is investigating a case where the prime suspect is a mysterious "helmet boy," the same person Hyun-heup saw in the building across from hers. In the end, Ji-wook kills the helmet boy, who was wearing special glasses that allowed him to see the red S Lines too.
Episode 2 — “Glasses of Truth”
S Line isn’t just a thriller—it’s an emotional rollercoaster. Episode 2 takes everything deeper: the mysterious glasses are now in more hands, red lines are showing up everywhere, and one devastating tragedy changes everything.
The story expands from curiosity to crisis, and we’re only at the beginning. The episode begins with more people gaining access to the mysterious glasses, those that reveal the red “S Lines” above people’s heads, indicating past intimate relationships.
Han Ji-wook's niece, Kang Seon-ah, gets her hands on the glasses. For a teenager, the power is intoxicating. But in this world, power doesn’t come without consequences.
Seon-ah decides to use the glasses to expose people’s secrets at school. She discovers that one of her classmates is involved in a secret relationship with a teacher and tries to blackmail them.
But the situation quickly spirals. When she pushes too far, the teacher retaliates. In one terrifying moment, Seon-ah is pushed off the school rooftop. As she lies injured, her red line—her only known connection—slowly fades. It’s heartbreaking.
Hearing a strange call from Seon-ah, Hyun-heup rushes to her school. When she arrives, it’s already too late. She finds herself injured, dying, and her red thread disappearing. The emotional weight of that moment crushes her and the viewers. This isn’t just about solving a mystery anymore. It’s personal.
Ji-wook now realizes the glasses are much more than strange tech—they're dangerous. His role as a detective shifts. He’s no longer just investigating people—he’s trying to find out who made these glasses, who’s distributing them, and why.
Lee Gyu-jin is the new teacher at Shin Hyun-heup’s school—and she’s not your typical educator. From the moment she arrives, there’s something off. She's calm, polished, and speaks in a way that makes you listen—but that serenity hides something much colder underneath.
She’s the kind of character who walks into chaos and doesn’t flinch. No visible red lines hover over her, which immediately makes her suspicious in a world where everyone seems to have at least one. That blankness? It’s eerie. It’s like her secrets are hidden on purpose.
People's reaction
K-drama lovers really like the style of the show—moody lighting, eerie background music, and a mystery that slowly pulls you in. It’s not just about relationships; it’s about the cost of exposing people’s pasts. Who has the right to know? What happens when the truth is out there—literally floating above your head?
It’s a bold concept, and while the show is just starting, the early episodes are enough to promise a wild, emotional ride ahead.
Final Thoughts
S line is not like other drama series, it is very different and interesting, I have never seen a concept like this.
The story moves slowly, but in a good way. You feel the tension build little by little. It’s not loud or fast, but it pulls you in with its strange mystery and quiet moments. The red lines are just one part—the real story is about how people react when hidden things come to light.
Lee Soo-hyuk plays his role well. He’s quiet, but you can tell a lot is going on inside. Arin brings emotion to her character, and Lee Da-hee adds a mysterious vibe that fits the tone of the show.
Personal Note
If you like dramas that take their time, with secrets, quiet emotions, and a strange twist, S Line might be just right for you.
Stick with us at New K-Drama—we’ve got more S Line twists, turns, and red threads coming your way. Don’t miss a moment!
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