Apart is a character who appears as an antagonist in the Death Row Prisoners Arc. A young man with light-colored hair often held back by clips, his appearance is unassuming, which belies his nature as a prolific serial killer. He was a death row inmate who was freed and recruited by the shadowy figure Slur to carry out a campaign of assassination and chaos. At first glance, Apart comes across as a quiet and even meticulous individual, but this composure masks a deeply disturbed psyche. He is a pronounced perfectionist with obsessive-compulsive tendencies, becoming visibly agitated by disorder, such as a single missing volume on a bookshelf, which he will immediately rectify even in the middle of a killing spree. This need for order extends to his murders, as he dismembers his victims with precise, clean slices and arranges their body parts in a neat, organized fashion. His cruelty is chillingly casual, having shown no remorse for his actions from a very young age, and he possesses a sick sense of humor, remarking that there is no better way to know a person than from the inside.

The driving force behind Apart's horrific actions is a desperate and twisted desire to connect with other people. As a child, he suffered from profound loneliness and neglect, particularly from his mother, while his father was the only one who showed him kindness and encouraged him to socialize. However, his introverted demeanor led to ridicule from other children, deepening his isolation. His father gave him a doll, which Apart used as a proxy for his bullies, methodically taking it apart to vent his anger. This behavior escalated to the dismemberment of a small animal. When his father discovered this, he took Apart to a doctor, and upon being told that his son was physically healthy, the father’s fear and disgust turned to rage. In a traumatic moment, Apart’s father pushed him away, shouting at him. Triggered by this rejection, Apart killed his father with a pair of scissors. In the aftermath, he looked inside the corpse and concluded that because they shared the same internal anatomy, he was finally connected to him and to everyone else. This became his warped logic: killing and taking apart a person allows him to see that they are all the same on the inside, thus forging a connection. He seeks out strong individuals, such as Taro Sakamoto, with whom he wishes to "connect" in this way, seeing his violence as a path to intimacy that he was always denied.

In the story, Apart is one of the primary obstacles sent by Slur, engaging in a major battle against Taro Sakamoto at Tokyo Tower. His role is to act as a deadly distraction as part of Slur's larger plan to overwhelm the assassin organization known as the Order. During his fight, Apart reveals his tragic past to Sakamoto, who rejects his philosophy, stating that killing only severs connections. Despite Apart’s attempts to kill him and endanger countless civilians by destabilizing the tower, Sakamoto defeats him but chooses not to kill him. Instead, Sakamoto brings the unconscious Apart back to his home and offers him a chance to change, mirroring Sakamoto's own journey from a legendary hitman to a peaceful life. This act of kindness is something Apart has never experienced. He finds himself treated with simple decency by Sakamoto, Shin, and the others, which leaves him shocked and uncharacteristically shy. In return for this trust, Apart provides valuable information about Slur's true intentions, revealing that the other death row prisoners were meant to be disposable distractions. This marks the beginning of a significant shift for Apart, who for the first time begins to experience a genuine, non-violent connection with others.

Apart's notable abilities center on his use of incredibly sharp, durable wires. He wields these with masterful precision, capable of effortlessly dismembering a person, slicing through metal and glass, or even catching projectiles and large falling objects. His fighting style relies entirely on these wires, using them to attack, defend, and restrain opponents from a distance. Apart possesses enhanced physical attributes, including immense durability to withstand punches from Sakamoto and superhuman reflexes. His obsessive nature, while a psychological vulnerability, also makes him a methodical and relentless fighter. Ultimately, his mental instability, combined with his perfectionism and desperate craving for connection, is both the source of his strength as a killer and his most profound weakness.