Junpei Yoshino attended Satozakura High as a withdrawn student bearing circular cigarette burn scars on his forehead—hidden beneath his hair—from relentless physical and psychological bullying. This abuse eroded his will to attend school. He resided with his mother Nagi Yoshino after his parents' divorce, sharing a close bond and frequently voicing concern over her smoking due to his trauma. Films provided his only solace, particularly horror franchises like *Scary Movie*; an attempt to start a film club ended when bullies commandeered it. Junpei’s innate perception of curses alienated peers but attracted the curse Mahito. After witnessing Mahito murder three bullies at a cinema, Junpei sought similar power. Mahito exploited Junpei’s trauma and resentment, surgically altering his brain to awaken latent jujutsu abilities. This granted Junpei control over cursed energy and the innate technique "Poison," manifesting as the jellyfish-like shikigami Moon Dregs (澱月, *Orizuki*), which paralyzed and poisoned targets via hair projections. Initially apathetic toward humanity—famously claiming he would kill everyone who hated him but not those he hated—Junpei’s cynicism softened after befriending Yuji Itadori. Bonding over film discussions, Junpei confided during a dinner that killing would "taint his soul." When Mahito framed Junpei’s bully Shota Ito for planting a Sukuna finger that caused Nagi’s death, Junpei donned his mother’s black jacket in mourning and unleashed Moon Dregs at school. He paralyzed classmates and tortured Shota before Yuji intervened. Their battle showcased Junpei’s tactical skill: he deduced Yuji’s physical prowess and deployed Moon Dregs defensively. Confronted about his mother’s death, Junpei challenged Yuji’s idealism, asking if "hearts" spawned curses. Yuji apologized for past insensitivity and invited Junpei to Tokyo Jujutsu High, vowing to find Nagi’s killer. Mahito interrupted, restraining Yuji and mocking Junpei’s naivety. Junpei recognized Mahito’s treachery too late; Idle Transfiguration mutated him into a distorted form. As Yuji begged Sukuna for aid, Junpei succumbed to injuries, whispering "Why?" before dying. His death cemented Yuji’s hatred for Mahito. Junpei’s shikigami Moon Dregs wielded poison-based cursed techniques. Though inexperienced, his rapid adaptability briefly matched Yuji in combat. Limited cursed energy reserves marked him as a novice sorcerer, yet strategic Moon Dregs usage revealed significant growth potential.