Episode 3 of "One High School Heroes" kicks off with Ui-Gyeom's father berating his employees over the lagging sales of medical equipment. Amidst the tension, he calls Ui-Gyeom and instructs him to accompany his mother for a weekend visit. Meanwhile, Seok-tae reassures his father that Ui-Gyeom is thriving in his new school environment.
Elsewhere, Ui-Gyeom finds himself engaged in a rooftop altercation with Ji-hyuk, ultimately emerging victorious. He employs Seung-joon's boxing combination to knock Ji-hyuk out, earning Seung-joon's admiration. Moved by Ui-Gyeom's prowess, Seung-joon decides to break away from the seniors and their combatant lifestyle. He urges Hong-II and Jin-woo to continue with the seniors if they wish to persist in their fighting antics, while he opts out.
Ji-hyuk reports back to his senior leader, Seung-sik, who leads a larger gang in search of Ui-Gyeom outside his academy. Seeking a conversation, Seung-sik confronts Ui-Gyeom, who inquiries if he's one of the two individuals Yoon-ki mentioned Ui-Gyeom must defeat to end the fighting. Ui-Gyeom's father arrives to pick him up, and during the ride home, he delivers a poignant lesson on power. He cautions Ui-Gyeom against being consumed by fleeting power and encourages him to pursue enduring power built through perseverance. Their destination? A suit shop for Ui-Gyeom's grandfather's birthday celebration over the weekend.
The next day at school, Ui-Gyeom confides in Yoon-ki about Seung-ki. Yoon-ki wisely advises Ui-Gyeom to refrain from engaging physically after his recent battle, allowing his body time to recuperate. When Seung-ki barges into Ui-Gyeom's classroom to provoke him, Ui-Gyeom heeds Yoon-ki's advice and bears the humiliation as Seung-ki dumps soda over him. Ui-Gyeom resists the urge to retaliate, earning Yoon-ki's commendation for his restraint.
Over the weekend, Ui-Gyeom joins his parents at his grandfather's birthday party, where the entire family, including his two aunts, gathers. During the meal, the sisters boast about their accomplishments, subtly hinting at their relief that Ui-Gyeom's father did not pursue a medical career. They suggest that if he had, they might have felt overshadowed by their father's preference for male offspring.
After the meal, Ui-Geum's grandfather singles him out and pressures him to accept a glass of wine, ignoring Ui-Geum's youthful age and initial refusal. With a stern command, the grandfather insists that Ui-Geum recount the tradition of learning to drink from elders, before pressing him to return to his old school, extolling its superiority over his current institution. Ui-Geum, desperate, warns that being forced back would be akin to a death sentence for him.
As Ui-Geum steps out of the house, his mind conjures an image of his elder brother standing at the far end of the compound. Reaching out with hope, Ui-Geum plummets into the swimming pool instead, prompting his father to dive in and rescue him, while his mother is enveloped in another bout of panic. Following this harrowing incident, Ui-Geum's grandfather lambasts his parents, leaving Ui-Geum with a profound sense of guilt for not confronting his grandfather's authority.
Driven by this newfound resolve, Ui-Geum confronts Seung-sik at school, defying Yoon-ki's wishes. He confesses his shame for not standing up to Seung-sik earlier and mirrors the humiliation Seung-sik once inflicted upon him by pouring cola over Seung-sik's head. Tempers flare, pushing them to the brink of violence, until the timely intervention of their homeroom teacher. Seung-sik retaliates with a chilling ultimatum: meet him at the band practice room for lunch, or face dire consequences.
At noon, Ui-Geum and Yoon-ki arrive at the designated spot, where Seung-sik presents Ui-Geum with a stark choice – join his ranks or fight. Ui-Geum, unwavering, chooses the latter. However, this confrontation finds Ui-Geum at a severe disadvantage. Seung-sik quickly gains the upper hand, choking Ui-Geum until he loses consciousness, leaving the scene tense and ominous.
