A crimson thread appears above the heads of those who have had a sexual relationship. When one of the connected individuals dies, the thread vanishes.

This is the eerie premise behind “S Line,” a webtoon by author Kkomabi, who also penned the original story behind the Netflix original series “A Killer Paradox” (2024). In this world, the most private of secrets — who has slept with whom — are laid bare.

“S Line” returns as an original series on streaming platform Wavve, but with a twist. Unlike the original, which begins when all of humanity suddenly starts seeing the threads, the drama shifts the focus to a few characters who have the special ability to see them.

Hyun-heup, played by Arin, a high school student, has seen the threads since birth. Others gain the ability through special glasses. Most people, however, remain unaware of the threads. Kkomabi said that Wavve's version expands the universe of the original story with new episodes and characters. “It was fascinating to experience the drama’s unique charm,” they added.

The series opens with Hyun-heup’s narration: “There are things in life that don’t need to be seen — no, things that mustn’t be seen. I have seen these lines since I was born.” Believing that her ability caused a tragedy in her family, Hyun-heup isolates herself.

One day, she witnesses a murder in her neighborhood. Suspecting a connection to the mysterious lines, she leaves the house. She then encounters glasses that allow the wearer to see the threads, just like she does. The story grows increasingly complex as she becomes involved with Detective Han Ji-wook, played by Lee Soo-hyuk, who is investigating the murder, and a mysterious teacher Lee Gyu-jin, played by Lee Da-hee, who has no threads at all.

The drama had its world premiere at the Grand Lumiere Theater during the 8th Cannes International Series Festival in May, where it was invited to compete in the long-form series category.

“S Line” also took home the Best Music award in its category — the first time a Korean production has earned that distinction at Canneseries. The score was directed by composer Lee Jun-oh, known for his work on films “The Terror, Live” (2013) and “Little Forest” (2018) and the Tving period drama series “Queen Woo” (2024).

Arin, a member of girl group Oh My Girl and an actress who has built her filmography through series like “Girl’s World” (2020) and “Alchemy of Souls” (2022), takes on a dramatically different role in “S Line.”

“When I first met Arin, I saw a determination in her to throw herself into the character, even into fire if necessary,” said director Ahn Joo-young at a press conference held at CGV Yongsan in central Seoul on Monday. “I felt like we could do anything together.”

“I thought, if not this work, when would I get to attempt something like this?” said Arin. “I really tried to show a different side of myself.”

Director Ahn, known for her 2018 indie feature “A Boy and Sungreen,” which portrayed youth in a non-stereotypical way, makes her fantasy-thriller debut with “S Line.”

“It feels surreal to win an award with a music director I’ve worked with since my short film days,” she said at the press event. “Each episode has a slightly different concept, so we tailored the tone with variations in instrumentation.”

“I love the original, but I couldn’t include every episode,” Ahn said. “At its core, 'S Line' is about people. I tried to show how individuals change through the existence of the line.”

“S Line” consists of six episodes, with the first two released on Wavve on Friday. Two new episodes will be released each week. Viewer discretion is advised due to scenes depicting self-harm and suicide.


Translated from the JoongAng Ilbo using generative AI and edited by Korea JoongAng Daily staff.
BY CHOI HYE-RI [kim.minyoung5@joongang.co.kr]