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The Mysterious Class
Promotional poster
Hangul
남고괴담
Lit.Ghost Story in a Boys' School
RRNamgogoedam
MRNamgogoedam
Genre
Developed byBamboo Network[1][2]
Written byHan Song-yi[1]
Directed byHa Han-me[2][1]
Starring
ComposerBaek Jong-sung et al.
Country of originSouth Korea
Original languageKorean
No. of seasons1
No. of episodes8[2]
Production
Executive producerYang Ji-hoon[1]
Producers
  • Kim Hwi-hwan
  • Song Yoon-geun
  • Jung Da-bin
EditorKim Jung-min
Running time15–23 minutes
Production companyYG Entertainment
Original release
NetworkYouTube[2]
Release12 November (2021-11-12) –
31 December 2021 (2021-12-31)

The Mysterious Class (Korean: 남고괴담[a]; RR: Namgogoedam; pronounced [ˈna̠mɡo̞ɡwe̞(ː)da̠m; ˈna̠mɡo̞ɡø̞(ː)da̠m]) is a 2021 South Korean web series featuring an ensemble cast consisting of the members of boy band Treasure—Choi Hyun-suk, Park Ji-hoon, Yoshinori Kanemoto, Kim Jun-kyu, Yoon Jae-hyuk, Asahi Hamada, Kim Do-young, Haruto Watanabe, Park Jeong-woo, So Jung-hwan, Mashiho Takata, and Bang Ye-dam. Its plot centers on a group of 12th grade students in a boys' school who try to solve the mystery of their class' resident ghost.[3]

The series aired for free viewing every Friday 22:00 KST on the band's official YouTube channel from 12 November to 31 December 2021.[4][5] Short clips containing post-credits scenes for each episode were also uploaded for paid subscription in the band's Weverse account a day after its corresponding episode's airing date.[6] It served as Treasure's first full-fledge endeavor in acting after the band made its acting debut through the short film It's Okay, That's Friendship[b] that was broadcast on 5 March 2021 as the 36th episode of their variety web series Treasure Map.[7][8]

Synopsis

[edit]

In Boseok Boys High School, the students of Grade 12 – Class 4 are trying to come into terms with the possibility of a ghost lurking in their homeroom after discovering that their class of 21 students was supposed to have only 20. A series of spooky events drove the students to suspect each other while trying to solve the mystery of their class' resident ghost, who might simply be posing as one of their classmates.[9][3]

Cast

[edit]

Main

[edit]

The roles of the main characters of the series are played by members of the boy band Treasure, including their two former co-members:[c]

  • Haruto Watanabe as Haruto
the resident ghost and former student of Grade 12 – Class 4 in Boseok Boys' High School; the late son of the school guard, Jae-hyuk's sole dorm roommate and Mr. Ha Dong-min's former classmate. Ten years prior to the events of the story, Haruto was a sickly student that rarely went to class due to his illness which ultimately led to his death, becoming the resident ghost of Grade 12 – Class 4. Ten years later, he became visible to the class' present batch of students and to its present homeroom teacher Mr. Ha, becoming the 21st "student" in a class that is supposed to have 20 students only. Yearning to have a normal school life "even after death", Haruto is fond of taking care of his classmates and enjoys taking photos of them using his Polaroid camera. Soon, his true identity is at risk of being exposed when his new classmates start looking for their class' resident ghost and begin suspecting each other.
  • Kim Do-young as Kim Do-young
the class president of Grade 12 – Class 4 in Boseok Boys' High School; Hyun-suk and Jung-hwan's dorm roommate. Do-young has a strong sense of rivalry against his class' top student Jae-hyuk due to being pressured by his father to perform well in academics in order to be able to have his college studies abroad. He is determined to find out the identity of their class' resident ghost but only for the prospect of gaining their homeroom teacher's recommendation if he manages the class well as its class president.
a student of Grade 12 – Class 4 in Boseok Boys' High School; Do-young and Jung-hwan's dorm roommate. Hyun-suk is interested in the paranormal and partnered with Ye-dam in doing a late-night séance that apparently revealed to the class the existence of a ghost in their homeroom.
a student of Grade 12 – Class 4 in Boseok Boys' High School; Asahi, Yoshinori and Mashiho's dorm roommate; an aspiring K-pop artist. Ye-dam was Hyun-suk's partner in a séance; he later discovers that a music demo he is working on has apparently been tampered by their class' resident ghost.
  • Asahi Hamada as Asahi
a student of Grade 12 – Class 4 in Boseok Boys' High School; Ye-dam, Yoshinori and Mashiho's dorm roommate. A quiet and introverted student, Asahi is a skilled painter who was suspected to be the class' resident ghost after his classmates discover a strange painting in the art room with his supposed signature.
  • So Jung-hwan as So Jung-hwan
a student of Grade 12 – Class 4 in Boseok Boys' High School; Do-young and Hyun-suk's dorm roommate; a YouTube vlogger by the name of Super King Cow Baby. Jung-hwan enjoys filming vlogs, although his videos do not gain traction.
  • Yoon Jae-hyuk as Yoon Jae-hyuk
a student of Grade 12 – Class 4 in Boseok Boys' High School; Haruto's sole roommate. As a top student, Jae-hyuk is very keen to studying and sometimes treats his less studious classmates coldly.
  • Yoshinori Kanemoto as Yoshinori
a student of Grade 12 – Class 4 in Boseok Boys' High School; Ye-dam, Asahi and Mashiho's dorm roommate. Yoshinori is into tarot card reading and doing magic tricks. He is the grandson of a mudang (female shaman).
  • Park Jeong-woo as Park Jeong-woo
a student of Grade 12 – Class 4 in Boseok Boys' High School; Jun-kyu and Ji-hoon's dorm roommate. Jeong-woo is an athletic boy who likes sports but is known to be a scaredy-cat among his classmates.
  • Kim Jun-kyu as Kim Jun-kyu
a student of Grade 12 – Class 4 in Boseok Boys' High School; Jeong-woo and Ji-hoon's dorm roommate. Jun-kyu has a bright and outgoing personality, and is a doting lover to his girlfriend.
a student of Grade 12 – Class 4 in Boseok Boys' High School; Jeong-woo and Jun-kyu's dorm roommate. Ji-hoon is a prankster who likes to scare his classmates.
  • Mashiho Takata as Mashiho
a student of Grade 12 – Class 4 in Boseok Boys' High School; Ye-dam, Asahi and Yoshinori's dorm roommate. Mashiho is a punctual student who regularly drinks milk for his growth plates.

Supporting

[edit]
  • Jang Tae-hoon as Ha Dong-min
the homeroom teacher of Grade 12 – Class 4 and an alumnus of Boseok Boys' High School; Haruto's former classmate. Mr. Ha was caught in an accident while working overtime coincidentally on the night his students, led by Hyun-suk and Ye-dam, did a séance. He trusted Do-young with the responsibility of managing the homeroom, promising him support in his overseas college career if he manages the class well. He is revealed to be a classmate of the late Haruto ten years prior to the events of the story.
  • Lee Kyung-min as Hong Sung-joon
a Grade 12 student in Boseok Boys' High School; Won-jin's classmate and an acquaintance of the students of Grade 12 – Class 4.
  • Chae Hee-soo as Son Won-jin
a Grade 12 student in Boseok Boys' High School; Sung-joon's classmate and an acquaintance of the students of Grade 12 – Class 4.
  • Seo Ye-ri as Lee Min-jung
a music teacher at Boseok Boys' High School.
  • Kim Hong-boo as Jung Geun-yong
a teacher at Boseok Boys' High School; Mr. Ha Dong-min and Haruto's former homeroom teacher. Mr. Jung is the teacher in charge of the school's milk rations. He is Mr. Ha's predecessor as homeroom teacher of Grade 12 – Class 4.
  • Han Myung-chul as Boseok Boys' High School's security guard
a staff at Boseok Boys' High School; Haruto's father. Deeply brokenhearted by his son's death at a such young age, he hid the funerary urn that contains Haruto's remains inside Haruto's own locker in the Grade 12 – Class 4 classroom where Haruto's ghost has been lingering since then.

Others

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  • Goo Shi-yeon as Jeong-woo's mother
  • Goo Jae-yeon as Yoshinori's grandmother, a mudang (female shaman)

Episodes

[edit]

The following table contains the episodes of the series:

No.TitleDirected byWritten byOriginal release date
1"There's a Ghost in Our Class"
Transliteration: "Uri bane gwisini isseo" (Korean: 우리 반에 귀신이 있어)		Ha Han-meHan Song-yi12 November 2021 (2021-11-12)
The students of Boseok Boys' High School Grade 12 – Class 4 run away in panic when a mysterious force apparently responded to their late-night classroom seance and, in their rush to escape, discover their homeroom teacher lying unconscious in the stairwell. Class president Do-young soon realizes that the result of the séance might be true after learning that their class of 21 is supposed to have 20 students only.
2"Who Could Be the Ghost?"
Transliteration: "Nuga gwisinilkkayo?" (Korean: 누가 귀신일까요?)		Ha Han-meHan Song-yi19 November 2021 (2021-11-19)
Class 4 becomes unnerved when a spooky voice resounds from Ye-dam's music demo. Do-young declares his strong opinion that they have to expel the ghost from their homeroom while paranormal geek Hyun-suk, one of the main participants of the séance, starts carrying out his plans to expose the ghost's identity.
3"The Ghost's Insidious Influence on Our Class"
Transliteration: "Gwisini uribane michineun yeonghyang" (Korean: 귀신이 우리반에 미치는 영향)		Ha Han-meHan Song-yi26 November 2021 (2021-11-26)
Upon being suspected as the class' resident ghost, an annoyed Asahi proves his classmates wrong with an irrefutable evidence of his innocence. Jae-hyuk secretly obtains a bujeok talisman from Yoshinori's shaman grandmother to counter a baleful presence that has affected his academic performance. An argument quickly ensues between Jung-hwan and Do-young over the former's late night live streaming of ghost hunting inside their classroom. After being accused by Asahi of being the resident ghost, Haruto gets burned by the bujeok that Jae-hyuk, his dorm roommate, had acquired from Yoshinori.
4"If You Pretend to be the Ghost ... The Ghost Itself Will Punish You."
Transliteration: "Gwisini cheok hamyeon ... gwisinhante honna." (Korean: 귀신이 척 하면... 귀신한테 혼나.)		Ha Han-meHan Song-yi3 December 2021 (2021-12-03)
Jae-hyuk asks Yoshinori if they could put another bujeok inside their homeroom. Jung-hwan resorts to filming "paranormal activity" that he had secretly contrived to cause fear among his classmates, desperate to gain more online following. Do-young confronts him anew, but Jung-hwan suspects that Do-young must be hiding something from the class. After Jae-hyuk makes a chilling discovery at his dorm room, Jung-hwan's attempt at getting back at Do-young backfires when the real ghost Haruto haunts him to give him a stern warning.
5"The Classroom That Is Truly Haunted"
Transliteration: "Jinjjaro gwisindeullin gyosil" (Korean: 진짜로 귀신들린 교실)		Ha Han-meHan Song-yi10 December 2021 (2021-12-10)
An unwitting Haruto allows Yoshinori to predict his future using tarot cards. Class 4 sets up a haunted house booth for the school's spring festival, though their first clients remain unflustered by their meager attempts to scare them. To save their booth, Haruto uses his powers to haunt the school building, but he scares both their next clients and his classmates in the process. When Class 4 manages to escape, they realize that Haruto and scaredy-cat Jeong-woo are still in the building.
6"Hide Well, The Ghost's Identity Will Be Discovered"
Transliteration: "Kkok-kkok sumeora gwisin jeongche deulkilla" (Korean: 꼭꼭 숨어라 귀신 정체 들킬라)		Ha Han-meHan Song-yi17 December 2021 (2021-12-17)
Haruto is gripped with guilt and the fear of rejection as Jeong-woo becomes hospitalized after accidentally getting injured and losing consciousness in the midst of Haruto's school-wide haunting at the school festival. Tensions rise among Class 4 students who start pointing fingers at each other, thinking the ghost intended to harm Jeong-woo. Haruto tries apologizing in person to Jeong-woo, who became mute due to trauma, but to no avail. While Haruto is not yet ready to open up and explain his side, Do-young discovers Haruto's true identity and exposes him to the class.
7"There's No Ghost In Our Class Anymore"
Transliteration: "Ije uribane gwisineun eopda" (Korean: 이제 우리반에 귀신은 없다)		Ha Han-meHan Song-yi24 December 2021 (2021-12-24)
Haruto is forced to admit his identity and reveal his tale to Class 4, but many of them do not believe in his innocence. While Haruto's father, the school guard, grieves for his late son, Class 4 remains divided on whether nor not to evict Haruto from the homeroom. Fueled by his failure to get their homeroom teacher's recommendation, Do-young plans to expel Haruto through a homeroom exorcism and initiates a poll, but Class 4 settles to keep Haruto in a narrow vote. Class 4's homeroom teacher finally realizes Haruto's identity and confronts him in a fit of rage.
8"Can We Be Friends With the Ghost?"
Transliteration: "Gwisin-gwa chin-guga doel su isseulkka?" (Korean: 귀신과 친구가 될 수 있을까?)		Ha Han-meHan Song-yi31 December 2021 (2021-12-31)
Class 4's homeroom teacher orders Haruto's desk to be taken out of the classroom and imposes a penalty to those who attempt to talk to Haruto or even just mention his name. While his father resigns for his sake, Haruto ultimately loses his visibility and physical form but continues showing care to his classmates. The class' sympathy for Haruto is put to the test when their homeroom teacher hires Yoshinori's grandmother to hold a ritual to exorcise the homeroom.

Soundtrack

[edit]

The soundtrack for The Mysterious Class consists of musical score composed by Baek Jong-sung et al. and the following two theme songs. Both of these theme songs are performed by Treasure and were released on 15 February 2022 through the CD version of the band's first extended play The Second Step: Chapter One.[13][14]

The Second Step: Chapter One (CD version)[14]
No.TitleLyricsMusicArrangementLength
5."BFF (Best Friends Forever)"
  • Q
  • Choi Hyun-suk
  • MGNTK
  • Q
  • MGNTK
3:22
6."Gonna Be Fine" (performed by Park Ji-hoon, Bang Ye-dam, Haruto Watanabe and Park Jeong-woo)Edle
  • Q
  • Modo
  • Modo
  • Q
  • MGNTK
3:55

A Christmas version of "BFF (Best Friends Forever)" was released earlier on 24 December 2021 through the band's official social media accounts.[15][16]

Notes

[edit]

References

[edit]
[edit]
Revisions and contributorsEdit on WikipediaRead on Wikipedia

The Mysterious Class

View on Grokipedia
from Grokipedia
The Mysterious Class (Korean: 남고괴담; RR: Namgogoedam) is a South Korean mystery thriller web series that premiered in 2021, featuring the members of the TREASURE as a group of 12th-grade students at an all-boys high school who discover a ghostly entity in their class after performing a , leading to mutual suspicions and a tense investigation to uncover the truth. The series blends elements of horror, , and teen , set in Class 4 of the 3rd year at the fictional Treasure High School, where an extra presence—bringing the student count to 21 instead of 20—triggers eerie events and forces the protagonists to question their peers' identities. Produced by YG Entertainment, the web drama consists of eight 20-minute episodes released weekly on Fridays at 10 p.m. KST, starting November 12, 2021, exclusively on TREASURE's official YouTube channel. The plot kicks off with a late-night "Bunshinsaba" ritual that summons a mysterious response, rendering their homeroom teacher unconscious and heightening the students' paranoia as they navigate alliances and betrayals to identify the ghost. The series quickly garnered attention, amassing nearly one million views on YouTube within half a day of its debut episode's release. The ensemble cast is led by TREASURE members including , , , Junkyu, Mashiho, Yoon Jae-hyuk, Asahi, , , Kim Doyoung, Park Jeong-woo, and So Junghwan, who portray the students alongside supporting roles like the homeroom teacher. Notable for showcasing the group's acting debut, The Mysterious Class earned an 8.3/10 user rating on MyDramaList from 5,016 reviews and a 6.8/10 on as of November 2025. The drama also features an original soundtrack, including the track "BFF" by , enhancing its thematic focus on camaraderie amid peril.

Premise and Setting

Plot Summary

The Mysterious Class is a mystery teen thriller web drama centered on the 12th-grade students of Class 4 at Boseok High School, an all-boys institution. The story begins when the students, portrayed by of , conduct a late-night that unexpectedly reveals the presence of a lurking among them. This discovery unleashes a cascade of eerie occurrences, prompting the group to embark on an investigation filled with suspicion and collaborative mystery-solving efforts. As events intensify within the , the core conflict revolves around the students' growing distrust of one another, which strains their friendships and tests the bonds of camaraderie unique to their all-boys environment. The narrative weaves thriller with themes of loyalty and unity, as the group navigates and uncovers clues to identify the spectral intruder. The plot culminates in a high-level resolution where the students successfully determine the ghost's identity and underlying purpose, bringing closure to the haunting mysteries and reinforcing their interpersonal connections, all while maintaining the story's atmospheric tension.

School and Atmosphere

The Mysterious Class is set in Boseok Boys' High , an all-boys institution that serves as a quintessential Korean high school environment, complete with rigid academic pressures and communal student life. The story centers on Grade 12, Class 4, a group of 20 students whose initially harmonious and isolated dynamic within the confines of their fosters a sense of camaraderie amid the broader school's bustling routines. This setup highlights the enclosed nature of the classroom as a microcosm of adolescent society, where everyday interactions like group study sessions and extracurricular activities underscore the theme of in a competitive educational landscape. The atmosphere is meticulously crafted to evoke and unease, blending realistic high school tropes with horror elements to heighten tension. Dim lighting and frequent nighttime scenes transform familiar spaces—such as corridors and classrooms—into shadowy realms that amplify feelings of isolation and vulnerability. , particularly the "Bunshinsaba" ritual for summoning spirits, is woven into the narrative, infusing the setting with cultural dread rooted in traditional ghost stories that resonate with local audiences. Activities like late-night study groups or school rituals, common in Korean teen dramas, are subtly twisted to evoke horror, turning mundane pressures of exams and friendships into harbingers of the . Thematically, the confined school environment explores through the lens of interpersonal drama and the , portraying Class 4 as a pressure cooker where youthful bonds are tested by unseen forces. The ghost's presence acts as a catalyst, disrupting the class's equilibrium and forcing confrontations with fear and suspicion in this isolated all-boys enclave. This fusion of everyday life with eerie undertones creates a pervasive mood of , emphasizing how the invades the ordinary routines of high school existence.

Production

Development and Announcement

The Mysterious Class was developed by in 2021 as a promotional web drama centered on the group , designed to highlight their acting abilities and interpersonal dynamics beyond music performances. The project originated as an extension of 's multimedia activities following their debut, leveraging the group's popularity to explore narrative storytelling. The screenplay was written by Han Song-yi. The web drama was officially announced on October 31, 2021, through YG Entertainment's channels, including , where a main featuring the cast in a eerie setting was unveiled. This reveal positioned the series as a mystery thriller drawing inspiration from traditional Korean high , or namgogoedam, evoking suspense within a school environment. All 12 members of were selected for the lead roles to emphasize their collective presence. Creative planning emphasized a concise 8-episode structure suited for short-form digital consumption, with weekly releases beginning November 12, 2021, on TREASURE's official YouTube channel at 10 p.m. KST. A key decision involved weaving TREASURE's music directly into the storyline, including original soundtrack contributions like the track "BFF" and unit songs such as "Gonna Be Fine," which served as thematic elements tied to character arcs. This integration aimed to blend the group's musical identity with the dramatic narrative for enhanced promotional synergy.

Filming and Crew

The Mysterious Class was produced as a web drama series in , with principal taking place in 2021 ahead of its premiere on November 12, 2021. The eight-episode run aired weekly on from November 12 to December 31, 2021, suggesting filming wrapped in the months prior to allow for . The series was directed by Ha Han-me, who helmed all eight episodes. Production was led by in collaboration with , with Yang Ji-hoon serving as executive producer and Kim Hwi-hwan, Song Yoon-geun, and Jung Da-bin as producers. Though detailed credits for the director of are not publicly listed, was handled by Kim Jung-min, contributing to the series' tight pacing across its 15- to 23-minute episodes. Post-production work on amplified tension through layered audio cues, such as subtle whispers and ambient echoes, to immerse viewers in the mystery without relying solely on visual scares. These choices aligned with the series' youth-oriented horror-thriller , prioritizing accessible production techniques suitable for a web format.

Cast and Characters

Main Cast

The main cast of The Mysterious Class consists of the 12 members of the K-pop group , who portray high school students in Class 4 experiencing events. The characters are named after the actors and draw on their to create authentic interactions amid the mystery. Choi Hyun-suk as Choi Hyun-suk, a paranormal enthusiast and roommate to Do-young and Jung-hwan, who conducted a séance with Ye-dam that revealed the ghost's presence. Park Ji-hoon as Park Ji-hoon, the prankster and roommate to Jeong-woo and Jun-kyu, who enjoys scaring classmates. Yoshi (Yoshinori Kanemoto) as Yoshinori, the tarot reader and magician, grandson of a mudang, and roommate to Ye-dam, Asahi, and Mashiho. Kim Jun-kyu (Junkyu) as Kim Jun-kyu, the outgoing student and roommate to Jeong-woo and Ji-hoon, known for being a doting boyfriend. Mashiho (Mashiho Takata) as Mashiho, the punctual student who drinks milk for growth and is roommate to Ye-dam, Asahi, and Yoshinori. Yoon Jae-hyuk as Yoon Jae-hyuk, the top student and Haruto's roommate, who is cold to less studious classmates and uses a against the . Kim Do-young (Doyoung) as Kim Do-young, the diligent and to Hyun-suk and Jung-hwan, who rivals Jae-hyuk academically and seeks to solve the mystery for a teacher's recommendation. Haruto (Haruto Watanabe) as Haruto, the resident ghost and former sickly student, late son of the , Jae-hyuk's , who loves photography and appears as the 21st student. Asahi (Asahi Hamada) as Asahi, the quiet painter and roommate to Ye-dam, Yoshinori, and Mashiho, suspected as the ghost due to a strange painting. Park Jeong-woo as Park Jeong-woo, the athletic but scared student, known as a scaredy-cat, and roommate to Jun-kyu and Ji-hoon. So Jung-hwan as So Jung-hwan, the YouTube vlogger under "Super King Cow Baby" and roommate to Do-young and Hyun-suk. Bang Ye-dam as Bang Ye-dam, the aspiring artist and roommate to Asahi, Yoshinori, and Mashiho, who partnered with Hyun-suk in the and finds a ghost-tampered music demo.

Supporting Cast

The supporting cast includes experienced South Korean actors portraying teachers, staff, and other students who contribute to the eerie school atmosphere and provide clues to the mystery. Jang Tae-hoon as Ha Dong-min, the homeroom teacher of Grade 12 Class 4 and a school alumnus, who trusts Do-young to manage the class and promises college support while offering subtle hints about the school's past. Kim Hong-boo as Jung Geun-yong, a stern teacher and former homeroom advisor who manages school supplies like milk rations, appearing in scenes of disrupted routines. Seo Ye-ri as , the music teacher whose appearances highlight the contrast between normal school life and the class's events. Han Myung-chul as the , Haruto's father who hid his son's urn in a school locker, delivering key backstory through family secrets. Lee Kyung-min as Hong Sung-joon, a Grade 12 student and acquaintance of Class 4 from another section, who shares rumors to introduce red herrings. Chae Hee-soo as Son Won-jin, another Grade 12 student acquaintance who provides external perspectives on strange events. Goo Shi-yeon as Park Jeong-woo's mother. Goo Jae-yeon as Yoshinori's grandmother, a mudang ( shaman). The supporting roles contrast the youthful main cast with adult authority figures, grounding the elements in realistic dynamics.

Episodes

Episode List

The Mysterious Class comprises eight episodes, released weekly on Fridays via the official TREASURE YouTube channel from November 12, 2021, to December 31, 2021. Each episode runs approximately 15-20 minutes, contributing to a total series runtime of about 2 hours. The episodes lack official individual titles and progressively build the central mystery of a potential ghost haunting the students' classroom, with non-spoiler synopses emphasizing the setup and escalating tensions without revealing key twists.
EpisodeAir DateSynopsis
1November 12, 2021The students of Class 4 at Boseok Boys' High are introduced through everyday school life, but peculiar incidents, including a , spark initial suspicions of an unseen presence among the 21 class members.
2November 19, 2021As strange noises and discrepancies persist, the class debates involving authorities and experiments with traditional methods to detect the anomaly, fostering early among the group.
3November 26, 2021The investigation intensifies with focused discussions on recent odd events, leading students to scrutinize classmates' behaviors and artifacts for clues to the classroom's secret.
4December 3, 2021Suspicions deepen as the group uncovers inconsistencies in their records and surroundings, prompting collaborative yet tense efforts to isolate the source of the disturbances.
5December 10, 2021Midway through their probe, the students confront escalating hints during routine activities, heightening paranoia and alliances within the class.
6December 17, 2021New evidence emerges from shared experiences, forcing the class to reevaluate their assumptions and intensify their search for the elusive .
7December 24, 2021Tensions peak as accumulated clues converge, pushing the students toward critical confrontations and revelations about their haunted environment.
8December 31, 2021The series culminates in the and resolution of the mystery, as the class unites to address the ghostly threat once and for all.

Key Plot Developments

Spoiler Warning: This section contains major plot spoilers for The Mysterious Class. The series opens with the students of Class 4 in an all-boys high school performing a late-night séance using the bunshinsaba spell, which summons a supernatural response and leads to their homeroom teacher's collapse after discovering discrepancies in student numbers—21 students listed but only 20 exam papers returned. Early episodes build suspicion through ghostly pranks, such as uneven soccer teams (11 versus 10 players), uneaten lunches, missing milk cartons, and a persistently cold classroom, prompting class president Doyoung and others to realize an extra, invisible presence lurks among them. These incidents escalate interpersonal tensions, with students like vlogger Junghwan filming suspicious events for his YouTube channel, further fueling paranoia and accusations within the group. In the mid-series arcs, revelations deepen the mystery tied to the 's history. A shaman spell provided by burns during an attempted use, exposing him as the who had been feigning normalcy, such as pretending to eat and subtly using powers like moving objects. 's backstory emerges as one of hidden sadness from his time as a dorm mate, concealed initially by a close friend, connecting his presence to unresolved traumas within the school environment. A key twist reveals Junghwan as an unexpected , staging fake hauntings—like using a remote for a and bloodied props—for online fame, diverting attention from the real threat while warns him via a mysterious to cease. Additional clues, including 's lack of shadow and corrupted audio files replaying the , solidify his identity and shift suspicions from others like Asahi, who is cleared after displaying religious artifacts. The finale centers on emotional confrontations and resolutions, as the students rally in support of despite the returning teacher's discovery of his ghostly nature and subsequent blame. Through a class vote, the group affirms their bond, allowing to remain, emphasizing themes of acceptance over fear. This arc transforms the narrative from horror-driven distrust to dramatic exploration of friendship's power in unraveling and healing mysteries, culminating in 's peaceful integration.

Music

Soundtrack

The original score for The Mysterious Class was composed by Jong-sung Baek, Hye-jin Kim, and Se-jong Kim, who crafted instrumental music to underscore the web drama's thriller elements. Produced by YG Entertainment's in-house team, the score integrates custom compositions that build tension during key sequences, such as investigations and paranormal encounters, without a dedicated vocal component. Unlike the theme songs, the was not released as a standalone OST album or singles but accompanied the episodes during their initial airing on from November to December 2021.

Theme Songs and Promotion

The web drama The Mysterious Class utilized two original songs by as its primary theme tracks: "BFF" (Best Friend Forever) served as the opening theme, highlighting the bonds of friendship among the protagonists in a mysterious setting, while "Gonna Be Fine" functioned as the ending theme, underscoring themes of resilience and positive resolution amid challenges. These tracks were prominently featured in the drama's teasers, episodes, and promotional materials to blend TREASURE's music with the storyline, enhancing narrative immersion. In December 2021, released a special "Happy ver." music video for "BFF," which incorporated clips from the series to extend holiday-themed promotion and cross-promote the group's discography. The integration of these theme songs significantly amplified TREASURE's visibility, as the drama garnered nearly 1 million views within half a day of its November 2021 premiere, drawing fans to both the series and the accompanying music. The tracks, initially teased through the drama, were later included on TREASURE's 2022 mini album THE SECOND STEP: CHAPTER ONE, with "BFF" performed live during their Japan tour concerts in –2023 to connect the project's themes to their stage shows.

Reception and Legacy

Viewership and Popularity

The web drama The Mysterious Class achieved substantial viewership shortly after its premiere, surpassing 10 million cumulative views on YouTube by the end of 2021 across its eight episodes released between November 12 and December 31. The series was primarily streamed for free on TREASURE's official YouTube channel, attracting a global audience with English subtitles available in fan uploads and official clips, though it was not officially hosted on platforms like Rakuten Viki. Peak viewership occurred with the premiere episode, which amassed over 11 million views, while subsequent episodes maintained strong engagement, ranging from approximately 4.8 million to 6.3 million views each.
EpisodeRelease DateViews (as of 2025)
EP.1Nov 12, 202111,168,011
EP.2Nov 19, 20216,336,839
EP.3Nov 26, 20215,665,841
EP.4Dec 3, 20215,098,346
EP.5Dec 10, 20215,377,390
EP.6Dec 17, 20214,961,569
EP.7Dec 24, 20214,770,013
EP.8Dec 31, 20215,008,826
The drama's popularity extended to robust fan engagement on social media, particularly among K-pop enthusiasts and international viewers in regions like Southeast Asia and Japan. Hashtags such as #MysteriousClass trended on platforms like TikTok and Twitter, inspiring fan-created content including edits, reaction videos, and informal challenges recreating suspenseful scenes from the series, such as ghost-hunting simulations. Discussions on Reddit and Weverse highlighted its appeal, with fans praising the blend of thriller elements and TREASURE's chemistry, fostering a dedicated online community that amplified its reach beyond initial YouTube streams. The series also contributed to TREASURE's commercial momentum, coinciding with heightened interest in their music and live performances. Following the drama's airing, the group saw increased visibility that supported their , with later releases like their second studio Reboot (2023) becoming their first million-seller and their 2025 mini-album LOVE PULSE surpassing 1 million in just four days, alongside bolstered demand for tour tickets in their subsequent world tours. This fan-driven success underscored the drama's role in solidifying TREASURE's international fanbase.

Critical Response and Impact

The Mysterious Class received generally positive reviews from audiences and critics for its successful fusion of horror elements with youth themes, particularly in portraying high school friendships amid suspense. On , the series holds an average rating of 6.8 out of 10 based on 171 user votes, with reviewers commending the engaging mystery plot and the ensemble cast's believable performances as students uncovering a ghostly presence. Similarly, on MyDramaList, detailed user critiques highlight the 's tight storytelling and emotional depth in blending thriller tension with relatable adolescent dynamics, earning scores ranging from 9.5 to 10 in several assessments. Critics noted some shortcomings, such as predictable plot twists and occasional unresolved subplots like the ghost's origins, which slightly diminished the suspense for more discerning viewers. One MyDramaList review awarded it a 6.0, pointing out unoriginal elements in the narrative and challenges in distinguishing characters due to similar acting styles among the idol cast. Despite these, the strong group chemistry and better-than-expected acting from members were frequently praised as standout features, with official reports describing the series as well-composed and entertaining. The did not garner major awards or nominations in K-drama competitions, as it was primarily a promotional project for the idol group rather than a standalone broadcast entry. However, it marked TREASURE's first full-fledged endeavor, showcasing members' versatility and opening doors to subsequent opportunities in web dramas and variety roles. In terms of broader impact, The Mysterious Class helped pioneer idol-led in the mystery-thriller genre, influencing a wave of similar productions featuring K-pop groups in the early . As a namgogoedam-style —focusing on tales in an all-boys high school—it contributed to the revival of this subgenre within K-content, encouraging more youth-oriented horror stories that leverage idol star power for accessibility and appeal. The drama's enduring legacy is evident in TREASURE's sustained success, including their 2025 achievements, highlighting its foundational role in building the group's global appeal.

References

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  32. https://www.allkpop.com/video/2021/12/treasure-drop-a-special-happy-christmas-ver-mv-for-the-mysterious-class-ost-bff-best-friend-forever
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