The ONE: High School Heroes Trailer: 5 Shocking Details That Prove It’s The Next Must-Watch Action K-Drama

The highly anticipated action K-drama, ONE: High School Heroes, has captivated audiences with its intense narrative and brutal portrayal of school violence, and the official trailer was the first sign of its explosive potential. As of today, December 18, 2025, months after the finale aired on Wavve, the series continues to generate massive buzz, especially regarding its potential renewal. The trailer successfully teased a dark, compelling story of a model student who leads a double life as a masked vigilante, setting the stage for one of the year’s most talked-about webtoon adaptations.

This eight-episode series, which premiered on May 30, 2025, and concluded on June 13, 2025, immediately drew comparisons to other popular school action dramas, but its unique focus on the protagonist's family trauma and the moral ambiguity of his actions set it apart. The trailer was a masterclass in tension, delivering quick cuts of intense fighting, emotional distress, and the stark contrast between the main character’s two worlds.

The Vigilantes: Complete Cast and Character Biographies

ONE: High School Heroes is based on the popular webtoon ONE by Lee Eun-jae. The series' success is largely attributed to its compelling ensemble cast, led by rising star Lee Jung-ha and the charismatic Kim Do-wan. The trailer highlighted the dynamic between these two central figures, one a vigilante and the other a skilled fighter who takes notice.

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• Lee Jung-ha as Kim Ui-gyeom: The protagonist. A model student with top grades who secretly transforms into a masked vigilante to combat the rampant school violence he witnesses. His motivation is deeply rooted in personal trauma and the oppressive control of his father.
• Kim Do-wan as Kang Yoon-Ki: A student at the same high school with excellent fighting skills and a keen ability to quickly assess situations. He becomes aware of Ui-gyeom’s actions, leading to a complex relationship.
• Kim Sang-ho as Kim Seok Tae: Ui-gyeom's father. He is portrayed as an oppressive figure whose control and pressure heavily influence Ui-gyeom's double life.
• Kim Joo-ryung: A key supporting role, though specific character details are often kept under wraps to build suspense.
• Lim Sung-kyun, Yuk Jun-seo, Yoo Hee-je, Lim Hyun-tae: Other significant cast members who portray students and figures involved in the school's power dynamics and violence.

1. The Dual Identity Reveal: A Model Student’s Dark Secret

The most shocking element prominently featured in the ONE: High School Heroes trailer was the stark duality of Kim Ui-gyeom. The initial shots presented him as the quintessential model student: humble, quiet, and focused entirely on his studies. This quickly shifts to a terrifying contrast. The trailer uses lighting and cinematography to show Ui-gyeom donning a mask, transforming into a brutal, efficient fighter who systematically takes down bullies.

This visual narrative immediately establishes the series’ core theme: the desperation that pushes a seemingly perfect student to embrace violence as the only means of justice. Unlike other school dramas where the protagonist is already a fighter, Ui-gyeom's transformation is fueled by a moral explosion—a breaking point where his natural fighting talent erupts against the relentless oppression. The trailer masterfully sells this transition, making the audience question the cost of becoming a hero in a broken system.

2. The Unseen Rival: Kang Yoon-Ki’s Intrigue

While the trailer focuses heavily on Ui-gyeom’s vigilante acts, it also introduces Kang Yoon-Ki (Kim Do-wan) as a pivotal figure. His presence in the trailer is less about direct combat and more about observation. Shots of Yoon-Ki intensely watching the aftermath of Ui-gyeom’s fights—or perhaps even the fights themselves—suggest that he is the only one who truly understands the gravity of the situation.

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Yoon-Ki is not just another student; he is described as having excellent fighting skills and a quick judgment of situations. The trailer hints at a complex relationship that is neither purely antagonistic nor entirely collaborative. This dynamic—the quiet, calculated observer versus the explosive vigilante—is a major hook. It suggests the series will explore a partnership or a rivalry that goes beyond simple fistfights, delving into the psychological toll of fighting school violence. This particular aspect of the trailer generated significant online discussion, with fans speculating whether Yoon-Ki would become an ally or a formidable obstacle to Ui-gyeom.

3. A Darker, More Realistic Webtoon Adaptation

The trailer’s gritty, raw aesthetic immediately signaled that the K-drama would take a more grounded and realistic approach compared to the original webtoon, ONE. While the source material is known for its action, the drama adaptation, as teased in the preview, grounds the violence in deep-seated family trauma.

The trailer includes brief but impactful glimpses of Ui-gyeom's turbulent home life, specifically his relationship with his oppressive father, Kim Seok Tae. This focus on the family drama—exposing the protagonist's brother's death early on—is a key difference from the webtoon that the trailer deliberately highlights. This creative decision was a smart move by the production team, Covenant Pictures and Very Good Studio, as it provides a more compelling emotional anchor for the vigilante's extreme actions. The trailer promises a story where the fight outside the school walls is just as brutal as the one inside his own home.

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4. The High-Octane Action Sequences and Cinematography

For an action K-drama, the quality of the fight choreography is paramount, and the ONE: High School Heroes trailer did not disappoint. It showcased incredibly fast-paced, visceral, and well-choreographed fight sequences. The trailer’s quick cuts of bone-jarring blows, combined with a pulsating soundtrack, immediately established a high-octane tone.

The cinematography, particularly the use of dark, shadowed hallways and dimly lit back alleys, emphasizes the clandestine nature of Ui-gyeom's vigilante activities. The production quality is reminiscent of other successful action thrillers, suggesting a high-budget effort to bring the webtoon's intense moments to life. This visual flair was a major selling point in the trailer, assuring viewers that the series would deliver on its promise of an action-packed, coming-of-age story that tackles heavy themes head-on.

5. The Unresolved Ending and Season 2 Speculation

Perhaps the most compelling detail the trailer inadvertently set up was the intense anticipation for an unresolved ending. With the series concluding its eight episodes on June 13, 2025, the finale was marked by an epic showdown that left a strong possibility for a second season. The initial trailer’s focus on the beginning of Ui-gyeom’s journey—his transformation and his encounter with Yoon-Ki—left a massive arc to be completed.

As of December 2025, the door for ONE: High School Heroes Season 2 remains wide open. The finale’s intense plot twists and the protagonist's unresolved conflicts with his father and the school system strongly suggest that the narrative is far from over. Fans are eagerly awaiting an official renewal announcement from the streaming platform Wavve. The success and high-quality production hinted at in the trailer make a second season a strong possibility, ensuring that the story of Kim Ui-gyeom and his fight against the darkness of his high school—and his family—will continue to be a hot topic well into 2026.