Episode 4 of One High School Heroes resumes right where the tension escalated, with Seung-sik's stranglehold on Ui-Geum leaving the latter unconscious. As Seung-ki braces himself for confrontation with the next target, Yoon-ki, Ui-Geum suddenly regains his senses. Warning Seung-ki with a steely gaze, Ui-Geum declares that any repeat of the chokehold will result in his demise. The stage is set for their rematch, and this time, Ui-Geum emerges victorious, overpowering Seung-sik.
Witnessing Seung-sik's impending defeat, his companion and fellow gang leader Sung-wook prepares to intervene, but Yoon-ki intervenes swiftly, halting his advance. Yoon-ki informs Ui-Geum that with Ji-hyuk taken care of, only two more opponents remain, suggesting an end to the fighting. He volunteers to handle the remaining contender personally.
Yoon-ki's prowess as a stealthy warrior unfolds as Sung-wook's punches barely graze him, while Yoon-ki demonstrates his superiority with each fluid move. The fight culminates in a spectacular "fans' benefits" roundhouse kick, leaving Sung-wook flat-footed. Meanwhile, Seung-ki takes a brief respite from his battle with Ui-Geum to observe the clash between Sung-wook and Yoon-ki. Returning to the fray, he vows to disable both combatants' hands as a grim warning to future adversaries.
Yet, Ui-Geum stands as an unyielding adversary. Refusing to relent, he counters Seung-ki's every move and concludes the skirmish by mirroring Yoon-ki's own "fans' benefits" kick, stunning the spectators. Ui-Geum then reapplies the chokehold on Seung-ki, rendering him unconscious once more, while reminding him of his earlier warning – a threat of mortality if his neck was ever threatened again.
Ui-Geum and Yoon-ki exit the band room with a stern warning etched into their minds: the rogue gang was严禁from perpetrating their malicious deeds within the school's premises ever again. Meanwhile, Ui-Geum's mother seeks solace at a psychiatrist's clinic, battling her persistent panic attacks. Desperate for relief, she pleads with the doctor to intervene, who advises her to confront the emotions she has been diligently avoiding. Back at home, Da-bin summons the courage to venture into Soo-kyum's room without succumbing to a panic attack, marking a significant step in her journey.
Elsewhere, in the confined space of a cram school, Ui-Geum's thoughts drift to his confrontation with Seung-ki, causing him to lose focus. The teacher, mirroring Ui-Geum's father's disciplinary style, reprimands him harshly, pushing his head back with a finger. Ui-Geum, no longer tolerating such treatment, stands up to the teacher, who responds by telling him to leave if he doesn't wish to learn. Ui-Geum, unperturbed, chooses to depart. Upon returning home, his father intensifies the scolding, decreeing that they will personally apologize to the cram school teacher the following day. Ui-Geum, though reluctant, acquiesces.
Later that evening, Ui-Geum reconvenes with Yoon-ki, who proposes a daring plan: to confront the school bullies, with their next target being someone from Ui-Geum's former school. Kim Nam-yeop, shielded by his father's status as a professor at a prestigious medical university, reigns terror over students, his misdeeds easily brushed under the rug. Yoon-ki envisions Ui-Geum joining him in restoring the sanctity of education by tackling these bullies head-on.
A grateful student approaches Ui-Geum, expressing how he has been bully-free since Ui-Geum dealt with Hong-II. However, Yoon-ki corrects the student's perception, emphasizing that Ui-Geum's actions were not driven by altruism but rather an outlet for the pressure he faced from his father, whom he couldn't confront directly.
Later, Ui-Geum's father forcibly escorts him to a gala attended by prospective candidates for a prestigious medical school, to which his elder brother had gained admission. Amidst the elite gathering, Ui-Geum encounters Nam-yeop, who sits at the focal table flanked by his father, the school dean, and other esteemed figures. Ui-Geum's father extols Nam-yeop's exceptional academic and athletic prowess openly, while Ui-Geum's mind is consumed by a haunting memory—a video of Nam-yeop bullying a disabled classmate at school. When prodded by his father to greet Nam-yeop, Ui-Geum instead inquiries about Wu Chengfan, asserting that Nam-yeop is far from being a beacon of innovation for the disabled; instead, he preys on their vulnerabilities. Nam-yeop's father attempts to dismiss these allegations as mere rumors, but Ui-Geum stands firm, citing the existence of videos as evidence. Embarrassed, Seok-tae promptly ushers Ui-Geum away from the table.
Ui-Geum confronts his father, declaring his reluctance to emulate his brother's footsteps. Elsewhere, Ui-Geum's mother unburdens herself to a psychiatrist, revealing that Soo-Kyum, despite his admission to medical school, committed suicide in his room a month later. Da-bin is overwhelmed with guilt, convinced she had glimpsed the warning signs yet ignored them, wishing she had heeded her son's silent pleas for help.
After the gala, Ui-Gyeom trudges through the rain to Yoon-ki's house, where they forge a pact to confront Nam-yeop together. Meanwhile, Nam-yeop continues his relentless bullying spree, unperturbed by his actions. The episode culminates with Yoon-ki and Ui-Gyeom, clad in matching brown shorts, hoodies, and crimson face masks, setting out on a mission to confront Nam-yeop.
