No. 13 is a secondary personality that emerges from the trauma of Juzo Murasaki, the protagonist of The Neighbor No. Thirteen. Juzo was subjected to severe bullying during his school years, culminating in an acid attack that left his face scarred. This traumatic event fractured his psyche, giving rise to No. 13, a violent and disfigured alter ego who embodies all of Juzo’s repressed rage and desire for revenge. No. 13 appears as a sinister, hooded figure with a scarred face, and he acts independently of Juzo, often haunting him as a separate entity. His primary motivation is to exact brutal revenge on Toru Akai, the former bully who has become Juzo’s boss and upstairs neighbor. No. 13 is vicious, cold, and entirely unrestrained, killing anyone who gets in his way, including Akai’s coworkers and family. He is also responsible for the death of Akai’s wife and toddler son. Throughout the story, Juzo struggles to control No. 13, but the alter ego grows increasingly powerful and takes over completely by the climax. In the film’s dual‑universe ending, No. 13 is revealed to be a product of a reality where Juzo never stood up to his bullies; in an alternate timeline, No. 13 still exists as a distant, watchful figure, suggesting he remains a permanent shadow of Juzo’s trauma. No. 13’s abilities are not supernatural but derive from unhinged physical aggression and a complete lack of moral restraint, making him a relentless and terrifying force.