Harry McQuinn is a high school student living in the United States and serves as the central figure of the series. He is originally portrayed as a quintessential social outcast, a loner with no friends who is frequently the target of bullying and cruel pranks by his peers, particularly members of the school's football team. Harry is depicted as being physically weak and unathletic, struggling to perform even a single pull-up, and he harbors a hopeless romantic affection for Catherine Chapman, a popular and beautiful student at his school.

In terms of personality, Harry is characterized by his social awkwardness, extreme peculiarity, and a pervasive sense of nervousness that borders on paranoia. He is often described as a "loser" by his classmates, an outsider who does not fit into the normal social structures of school life. His personality is also noted for its lack of assertiveness; he appears perpetually dumbfounded by the concept of responsibility and fails to take initiative to resolve the problems that his emerging abilities create. His resemblance to characters like Shinji Ikari is noted as being only visual, as Harry lacks the same degree of internal struggle or proactive character development.

Harry's role in the story is triggered by a traumatic event in which he witnesses Catherine being attacked by bullies. In a moment of desperation, his latent psychic abilities awaken, granting him powerful telekinetic powers. This discovery instantly transforms his life, making him an object of intense interest to Catherine, who begins to experiment with his newfound abilities. However, his powers come with a horrific and uncontrollable side effect: every time Harry uses his psychic abilities, a person in the vicinity dies a violent death, often by having their bodies twisted or crushed. This tragic flaw transforms him from a simple victim into an unwilling danger to everyone around him. His primary motivation throughout the narrative stems from his infatuation with Catherine, though he is also driven by the desire to understand and control the frightening powers he never asked for.

Regarding key relationships, Harry's life revolves around Catherine Chapman, his love interest, who is both fascinated and horrified by his powers. Her curiosity and encouragement lead him to demonstrate his abilities, inadvertently setting the stage for disaster. He also interacts with John Mayfield, Catherine's sort-of ex-boyfriend, who is protective of her and views Harry with suspicion and jealousy. On a broader scale, Harry becomes a target for a mysterious organization known as Accuser, which seeks to capture and exploit his dangerous abilities for its own ends. Scientists such as Kate and Meryl Newman are involved in these efforts, viewing him as a valuable test subject.

In terms of development, Harry is portrayed as an "unskilled but strong" psychic. He begins with no conscious control over his telekinesis, and even when he learns to manifest it, his mastery remains crude and volatile. He does not undergo a typical heroic transformation; instead, he remains a passive figure, largely unable to manage the escalating tragedy around him. His most notable and tragic development is the realization of the consequences of his powers, particularly after a catastrophic event where he accidentally kills a large number of spectators during a television demonstration of his abilities.

Harry's notable ability is telekinesis, which allows him to move and manipulate physical objects with his mind. His power is shown to be extremely potent, capable of bending spoons and hurling large objects over great distances with ease. However, his ability is defined by its lack of control. A defining and unique aspect of his power is its side effect: the unintentional and violent deaths of nearby people whenever he uses it. This makes his psychic ability as much a curse as a gift, turning him into an unwitting perpetrator of mass murder.