Episode 6 of "ONE: High School Heroes" picks up right where we left off, with Ui-Gyeom caught in a frenzy as he relentlessly pounds In-Kyu. In-Kyu pleads desperately for mercy, but Ui-Gyeom, consumed by the haunting memories of his brother and father, continues his onslaught until Yoon-ki intervenes, pulling him back forcefully. Yoon-ki urges Ui-Gyeom to regain his composure, reminding him that they can't stoop to being the villains.
Later, Yoon-ki receives a call informing him that Ji-Sung has regained consciousness at the hospital. Without hesitation, Yoon-ki rushes off to be by his side. Meanwhile, as Ui-Gyeom waits for the train, he eavesdrops on a group of students discussing a viral video featuring them. The students propose compiling a list of all the troublemakers at their school so that the masked heroes can deal with them accordingly.
At the hospital, Ji-Sung is unable to speak, but his eyes light up with recognition when he sees Yoon-ki, filling Yoon-ki with elation that his friend is awake. On their way out, Yoon-ki reveals that he has two more names on his hit list and vows not to let them escape justice.
Back home, Da-bin engages in a phone conversation and agrees to start a new job the following week. Seok-tae arrives shortly after and informs her that he's arranged for someone to clean Soo-Kyum's room the next day. He remains vague about the cleaner's identity, only mentioning that the room has been a distraction for Ui-Gyeom.
Da-bin confronts Seok-tae, questioning whether he's noticed Ui-Gyeom returning home with injuries lately. She's furious that Seok-tae only seems to care about the results, pushing Ui-Gyeom relentlessly just as he did with Soo-Kyum. Now, Ui-Gyeom is getting embroiled in fights, and Da-bin is worried about the toll it's taking on him.
Upon arriving home, Ui-Gyeom is met with Seok-tae's demand to hand over the Walkman. Ui-Gyeom stands his ground, refusing to comply, but Seok-tae persists relentlessly. Ui-Gyeom reveals that the Walkman is a cherished treasure belonging to his brother, and accuses Seok-tae of constantly pressuring him to emulate Soo-Kyum. With a mixture of defiance and vulnerability, Ui-Gyeom explains that the Walkman held a special place in his heart because the music it played could transport him to a realm free from the shadow of his father. Seok-tae is left momentarily speechless, taken aback by Ui-Gyeom's revelation. Undeterred, Ui-Gyeom continues, blaming his brother's untimely demise on their parents.
The next day, Yoon-ki enlists Ui-Gyeom's help to confront the third target on their list, Pi Dao-yi. However, Dao-yi is no stranger to their vigilante tactics and is lying in wait for them. This time, Ui-Gyeom and Yoon-ki find themselves outmatched and overwhelmed. As Dao-yi and his gang tear off their red masks, Dao-yi immediately recognizes Yoon-ki. He questions whether Yoon-ki's pursuit is fueled by a desire for vengeance against Ji-Sung, who lies injured in the hospital.
Realizing they're no match for their opponents, Ui-Gyeom and Yoon-ki make a desperate bid to flee. Dao-yi and his gang give chase, hot on their heels. Seung-joon, who happens to be making deliveries as part of his part-time job, spots them being pursued and offers them a ride to safety. Ui-Gyeom is furious with Yoon-ki for keeping the revenge motive a secret from him. Moreover, his injuries are now glaringly obvious, making it impossible for him to return home. Ui-Gyeom pleads with Seung-joon to let him crash for the night.
Seung-joon, understanding the gravity of the situation, takes Ui-Gyeom to the boxing gym where he can spend the night. He, too, cannot risk taking Ui-Gyeom home, as it would only alarm his parents. As they settle in, Ui-Gyeom is surprised to discover that Seung-joon is quite talkative, a stark contrast to his aloof demeanor at school. Seung-joon reveals that he was once a top-ranked boxer before enrolling in high school. However, his life took a turn when he started hanging out with Hong-II and Seung-ki, leading him down a path of trouble. Had he not strayed, he would have been diligently preparing for the Asian competition.
Seung-joon issues a word of caution to Ui-Gyeom about his association with Yoon-ki. He advises Ui-Gyeom to either drown out the world with his headphones and focus on his studies as he used to, or to channel his energy into boxing instead of engaging in street fights. Meanwhile, Ui-Gyeom ignores his parents' frantic calls. He sends his father a text message stating that he will be spending the night at a friend's place and then switches off his phone, seeking solace in the temporary refuge he has found.
Meanwhile, Nam-yeop, In-kyu, and Dao-yi hastily report Yoon-ki's recent string of ambushes to Ki-soo. As it unfolds, the truth emerges that these four individuals were the very ones behind the heinous act that befell Ji-Sung, an incident that sent him spiraling into a hospital bed and a coma that stretched over two long years. Desperate to offload the burden, they implore Ki-Soo to step in and deal with Yoon-ki and Ui-Gyeom. Ki-soo, ever the opportunist, seizes the moment to demand a higher price from Nam-Yeop for his services this time around.
The following day, Ki-soo makes his grand entrance at school, striding purposefully into Seung-ki’s band room. Inside, he unleashes his wrath on an unsuspecting student, mercilessly torturing him in a bid to extract information about Yoon-ki's whereabouts. Yet, the student remains clueless, unable to provide the answers Ki-soo seeks. Just then, Seung-ki and his loyal crew burst into the room. Ki-soo, unfazed, issues a direct order for them to bring Yoon-ki to him. Seung-ki, ever the daredevil, lunges forward as usual, but his bravado is swiftly met with Ki-soo's brutal fist, leaving him battered and beaten.
As the episode draws to a close, a member of Seung-ki's crew frantically calls Yoon-ki and Ui-Gyeom to the room. Ui-Gyeom, fueled by his usual fiery spirit, is eager to charge headlong into the fray and confront Ki-Soo. However, Yoon-ki, with a steely resolve, steps in and commands him to stand back. Yoon-ki is determined to shield Ui-Gyeom from the escalating conflict, unwilling to let him be dragged into his personal vendetta with Ki-soo.
