Episode 7 of "ONE: High School Heroes" opens with a poignant flashback to the day Ji-sung found himself in the hospital. Yoon-ki and Ji-sung had once shared a school with the likes of Pi Daoyi, In-kyu, Nam-yeop, and Choi Ki-soo, who were notorious high school bullies in their previous institution. These bullies targeted Yoon-ki and Ji-sung, accusing them of beating up some of their juniors. They coerced Yoon-ki and Ji-sung into becoming their underlings, demanding they extort money from fellow students and hand over a portion to the bullies.
When the time came to report to the bullies, Ji-sung adamantly refused to contribute anything, while Yoon-ki, fearing for his safety, handed over some cash. The bullies, satisfied with Yoon-ki's compliance, let him go but continued their relentless harassment of Ji-sung, who ultimately plummeted from a rooftop in a desperate bid to escape.
Fast forward to the present, and Yoon-ki finds himself face-to-face with Ki-soo, though he lacks the strength to stand up to him. Ui-Gyeom attempts to intervene, but Ki-soo inflicts a severe shoulder injury on him. Just as Ki-soo is about to cripple Ui-Gyeom's legs, Lee Geol-jae makes a dramatic entrance. Unwilling to engage in a fight with Geol-jae, Ki-soo retreats.
Ui-Gyeom loses consciousness and drifts into a memory of his brother's final days. Soo-kyum had endured similar hardships with their overbearing father. He had tried to confide in his mother, expressing his exhaustion and desire to quit medical school, but his pleas were ignored. Time and again, Soo-kyum's erratic behavior escalated, leading him to strangle Ui-Gyeom or hurl objects in a fit of rage.
Seok-tae and Da-bin dismissed Soo-kyum's outbursts, attributing them to the immense pressure he faced at school. Eventually, Soo-kyum reached his breaking point and took his own life by jumping out of a window. He did so moments after slipping his Walkman to Ui-Gyeom, who pretended to be asleep.
Ui-Gyeom awakens in the hospital, revealing to his father that Nam-yeop had dispatched henchmen after him in retaliation for Ui-Gyeom's intervention against the bullies. Ui-Gyeom challenges his father, asking if he's willing to send Nam-yeop to the hospital in retaliation, considering Nam-yeop is the son of his most prominent client.
Meanwhile, Ki-soo offers a heartfelt apology to Ui-Gyeom for dragging him into his vendetta. Ui-Gyeom, however, remains uninterested in the feud between Ki-soo and Yoon-ki. His sole concern is retrieving his Walkman, which Ki-soo had taken. Yoon-ki pleads with Ui-Gyeom not to pursue Ki-soo, prompting Ui-Gyeom to question why Yoon-ki had initiated a fight he knew he couldn't win.
The following day, as Seok-tae makes his way out of the office, Yoon-ki trails closely behind. Seok-tae, with a stern expression, instructs Yoon-ki to keep his distance from Ui-Gyeom, revealing that Ui-Gyeom is set to study abroad as soon as he completes his military discharge. Yoon-ki, burdened by guilt, feels a heavy weight on his shoulders for the misfortune that has befallen Ui-Gyeom. Seung-joon exacerbates Yoon-ki's distress by accusing him of leading a model student into a brawl that ultimately landed him in the hospital. Seung-joon challenges Yoon-ki, questioning whether he can truly call himself Ui-Gyeom’s friend.
Later, Yoon-ki pays a visit to Ji-sung at the hospital. To his relief, Ji-sung has regained consciousness and is now able to sit up on his own and engage in conversation. Yoon-ki, overwhelmed with remorse, apologizes profusely to Ji-sung for abandoning him in his time of need. He berates himself, believing that the bullies had thrown Ji-sung off the roof because he wasn't there to protect him. However, Ji-sung, with a gentle smile, reassures Yoon-ki not to blame himself.
Ji-sung explains that he knew Yoon-ki had attempted to return for him, but the bullies had intended to target Yoon-ki instead. In a courageous act, Ji-sung had stepped in to shield Yoon-ki from harm. Furthermore, thanks to the police statement Ji-sung provided, his father was able to initiate a lawsuit against those responsible for the assault.
Meanwhile, Ui-Gyeom, lying in his hospital bed, experiences a hallucination. He sees his brother by his side, leaving behind a Walkman. Startled, Ui-Gyeom awakens and follows the phantom image up to the rooftop. Da-bin, upon waking and discovering Ui-Gyeom's absence, panics. She rushes to the rooftop and finds Ui-Gyeom perched precariously on the edge. Ui-Gyeom turns to Da-bin, his eyes reflecting a deep understanding, and utters the very words Soo-kyum had once spoken to her, which she had dismissed.
Da-bin, struck by the realization, suffers a panic attack, struggling to catch her breath. Ui-Gyeom, sensing her distress, reaches out to help her up. In that moment, Da-bin makes a solemn vow to protect Ui-Gyeom from any further harm. Thus, when Seok-tae arrives at the hospital to inform Ui-Gyeom of his impending departure to the States, Da-bin stands her ground. She confronts Seok-tae, revealing that Ui-Gyeom had nearly leapt off the rooftop and declares her unwavering commitment to safeguard her son.
At the episode's climax, Ki-soo’s gang descends upon Geol-jae after school, their intentions malicious. One of them, with a cruel swing, strikes Geol-jae with a flowerpot, dislocating his shoulder in the process. Ki-soo arrives on the scene just as his minions have inflicted the injury, and they prepare for a one-on-one confrontation, the tension palpable in the air.
