The premiere of "One High School Heroes" kicks off with Kim Ui-Gyeom accompanying his father to the school office, where they meet Ui-Gyeom's new homeroom teacher. Kim Seok-tae eagerly extols his son's versatility and exceptional abilities, reassuring the teacher that Ui-Gyeom will seamlessly integrate into his new academic environment.
The homeroom teacher then escorts Ui-Gyeom to his classroom, where they encounter Kang Yoon-ki, a fellow student who arrives just in the nick of time. Ui-Gyeom introduces himself to the assembled classmates and takes a seat at the rear of the room. Addressing the class, the teacher highlights Ui-Gyeom's status as a former top student, urging everyone to foster a friendly rapport with him.
Hong-II, a curious classmate, expresses his bewilderment about why a star pupil would opt to transfer to their seemingly ordinary school. Once the teacher exits the classroom, Ui-Gyeom dons his headphones, an action that promptly irritates Hong-II, who misinterprets it as Ui-Gyeom's attempt to shun the group. Jin-woo, another student, steps in to advise Hong-II to steer clear of any trouble with the new arrival.
After the school bell rings, Ui-Gyeom heads to his after-school tutoring session. On his way back home, he receives a message from his father, informing him of a delay and instructing Ui-Gyeom to complete his homework and share it via social media. Arriving home, Ui-Gyeom inquiries about taking his mother's medication, but she expresses concern, prompting Ui-Gyeom to relent.
Later in the night, Seok-tae finally arrives home. Without wasting a moment, he heads straight to Ui-Gyeom's room to keep tabs on his homework progress. Ui-Gyeom encounters a blunder in his assignments, prompting his father to intently supervise as he tackles the problem anew until mastery is achieved. Once his father exits the room, Ui-Gyeom finds himself resorting to a desperate act of self-harm, attempting to choke himself into unconsciousness.
The following morning at school, Ui-Gyeom walks in on a distressing scene where Hong-II and Jin-woo are bullying Ming-Syeop, simply because he failed to buy them bread. Ui-Gyeom takes his seat and retrieves the career form distributed the previous day. His father had scrutinized it and noted Ui-Gyeom's aspiration to become a doctor, much to Ui-Gyeom's frustration as he glares at the paper. Just then, Hong-II exacerbates the tension by forcing Ming-Syeop to carry him around the classroom like a throne. In the chaos, Hong-II inadvertently knocks over Ui-Gyeom's cherished Walkman. Hong-II's relentless bullying of Ming-syeop brings back haunting memories of Ui-Gyeom's own oppressive encounters with his father. Unable to bear it any longer, Ui-Gyeom loses his composure and shouts at Hong-II, prompting Hong-II to retaliate with physical violence until Jin-woo intervenes.
After school, Hong-II, Jin-woo, and Seung-joon corner Ui-Gyeom on his way home. They hustle him aside and strip him of all his money. Hong-II inserts his contact number into Ui-Gyeom's phone, commanding him to answer within ten seconds whenever he calls. Ui-Gyeom pleads his inability to answer after school hours, but Hong-II responds with a harsh slap. Meanwhile, Seung-joon watches Ui-Gyeom closely, noting an unusual lack of fear in his demeanor.
Back at home, Ui-Gyeom repeats his daily ritual under his father's stern oversight, once again attempting to choke himself in despair. Hong-II texts Ui-Gyeom, demanding he bring bread, a request Ui-Gyeom ignores. In class, Hong-II confiscates Ui-Gyeom's Walkman as punishment for his disobedience. Ui-Gyeom begs for its return, explaining its sentimental value, but Hong-II deliberately drops it to the ground and stomps on it. This final straw ignites Ui-Gyeom's fury, leading to an intense altercation where Ui-Gyeom beats Hong-II relentlessly until he is incapacitated.
Kang Yoon-ki, captivated by Ui-Gyeom's demeanor, approaches him after the school bell rings, inquiring about his strategy for dealing with Hong-II's henchmen. Ui-Gyeom responds with a serene assurance that he harbors no intentions of engaging in a brawl, to which Yoon-ki scoffs, branding his attitude as naivety. As Ui-Gyeom traverses the path to his cram school, contemplation over the impending altercation fills his mind, bringing him a peculiar sense of exhilaration. So engrossed is he in his thoughts that he narrowly avoids missing his stop. Arriving home, his father awaits, reminding him of the looming tests, an anchor pulling him back to reality.
The Walkman, a cherished possession bestowed upon Ui-Gyeom by his elder brother Soo-Kyum, holds immense sentimental value. Recalling a heartfelt conversation with Soo-Kyum, Ui-Gyeom finds himself envisioning his brother's presence in his room. However, this illusion is shattered as his father enters, dispelling the illusion.
The next morning, at school, Hong-II reignites the conflict, squaring off against Ui-Gyeom once more. Ui-Gyeom offers an apology for their previous encounter, but Hong-II, driven by a thirst for revenge, remains unrelenting. Yoon-ki attempts to counsel Ui-Gyeom on his next steps as Hong-II and his cronies prepare for another confrontation. Ui-Gyeom stands firm, refusing to be swayed by the prospect of violence.
Seung-joon, leading Hong-II and Jin-woo, confronts Ui-Gyeom in the washrooms. With an authoritative tone, Seung-joon demands Ui-Gyeom kneel, but Ui-Gyeom digs in his heels, locking eyes with Seung-joon in a defiant stare. The homeroom teacher's unexpected arrival interrupts the tense confrontation, bringing an end to the brinksmanship. He turns to Yoon-ki, who had been an onlooker, instructing him to escort Ui-Gyeom to the infirmary for assessment.
Back in the classroom, Yoon-ki persists in his conversation with Ui-Gyeom, mentoring him on how to tackle Seung-joon in a confrontation. He unequivocally states that Ui-Gyeom stands no chance in a straight-up fistfight against Seung-joon and suggests instead that he aim to immobilize him. Ui-Gyeom firmly declares that he does not engage in fights and pleads with Yoon-ki to cease his advice.
As the school day draws to a close, Hong-II snatches Ui-Gyeom's Walkman. He phones Ui-Gyeom, summoning him to the very spot where they had previously roughed him up. Ui-Gyeom feels an urge to rush to the rendezvous, but Yoon-ki warns him against it, pointing out that he'd be too worn out to defend himself.
At the agreed meeting place, Seung-joon issues Ui-Gyeom a challenge: a fight with his Walkman as the stake. Initially, Seung-joon appears confident and in command, unaware that Ui-Gyeom is meticulously observing his every move, seemingly submitting himself as a human punching bag. As the episode reaches its climax, Ui-Gyeom deftly dodges one of Seung-joon's punches and delivers a powerful blow squarely to his face, setting the stage for an unexpected twist in their rivalry.
