“S-Line” K-Drama Explained: Webtoon Differences, Cast, Fan Reactions & Where To Watch (2026)

Viewers describe K-Drama “S-Line” as brilliant but disturbing. The award-winning drama dropped its first two episodes on July 11th and has already caused a stir online.

“S-Line” is adapted from the popular webtoon written by Kkomabi, the same author of Netflix’s “A Killer Paradox.”

Starring Lee SooHyuk, Lee DaHee, Arin, and Lee EunSaem, the drama depicts a world where you can see a red line that connects sexual partners using a mysterious eyeglass.

It is directed by Ahn JooYoung and written by Hwang HoGil and Kim JoonHyun. The drama was the only Korean title selected for the main competition at the 8th Cannes International Series Festival, where it won Best Music.

Before it drops the other two episodes on Friday, let’s take a look at why the drama is causing a frenzy by diving into the plot, characters, fan reviews, webtoon ending, and where to watch.

Plot of “S-Line”

Since birth, Shin HyunHeup (played by Arin) can see the S-Line, or the red line connecting people with sexual relationships. When she was young, she didn't know what the line meant. As she realizes the meaning of the line, she decides to keep it to herself and hide from the world.

However, everything becomes complicated when she finds out that her middle school friend Kang SeonA (played by Lee EunSaem) has an eyeglass to see the lines and tries to abuse it.

Cast and Characters of “S-Line”

Arin as Shin HyunHeup

Shin HyunHeup has an innate ability to see S-lines. Her mother killed her father when she was young, after she drew the S-lines of her father. From then on, she believed she was cursed and attempted suicide several times.

She lived as a hikikomori (someone with severe social withdrawal) until she realized that her ability had a positive side and gained the courage to go out into the world.

Lee SooHyuk as Han JiWook

Han JiWook is a detective from the 2nd Violent Crimes Unit of Bangju Police Station. He is also Shin HyunHeup's neighbor. He lives with his niece Kang SeonA but barely cares about her.

He has had physical relationships with so many women that he has countless S-lines above his head.

Lee DaHee as Lee GyuJin

Lee GyuJin is an ethics teacher at Bangju High School and Kang SeonA's homeroom teacher. She has no S-line.

She is a mysterious character who appears naive and clumsy but sometimes shows a sharp side.

Lee EunSaem as Kang SeonA

Kang SeonA is Han JiWook's niece and a student at Bangju High School. She has one S-line and is being bullied by Kim HyeYoung's gang.

Her goal is to quickly make money and become independent.