"Kiznaiver" is set in the fictional Japanese city of Sugomori, where a secret government experiment known as the Kizna System connects individuals through shared pain. The system links the physical and emotional pain of its participants, creating a network where injuries or emotional distress experienced by one member are felt by all. The experiment aims to foster empathy and unity among people by forcing them to share their suffering.

The protagonist, Katsuhira Agata, is a reserved and emotionally detached high school student who becomes one of the Kiznaivers. Alongside him are six other students: Noriko Sonozaki, a mysterious girl with a deep connection to the Kizna System; Chidori Takashiro, Katsuhira’s childhood friend who harbors unrequited feelings for him; Hajime Tenga, a hot-headed delinquent; Nico Niiyama, a quirky and eccentric girl; Tsuguhito Yuta, a calm and calculating honor student; Honoka Maki, a seemingly perfect but emotionally distant girl; and Yoshiharu Hisomu, a carefree and enigmatic boy with a fascination for pain. Each character represents a different personality type, and their interactions are shaped by the forced connection of the Kizna System.

As the story progresses, the group is tasked with completing missions designed to test their bonds and deepen their understanding of one another. These missions often reveal personal struggles, traumas, and insecurities, forcing the characters to confront their own vulnerabilities and the pain of others. The Kizna System’s true purpose becomes a central mystery, with Noriko’s involvement and the origins of the experiment gradually coming to light. The narrative explores themes of empathy, human connection, and the nature of pain, both physical and emotional.

The dynamics within the group evolve as they navigate their shared experiences, leading to moments of conflict, camaraderie, and self-discovery. Katsuhira’s emotional growth is particularly significant, as he begins to reconnect with his feelings and confront his past. The series balances its sci-fi premise with character-driven drama, emphasizing the emotional and psychological impact of the Kizna System on its participants. The story concludes with the group confronting the truth behind the experiment and its implications for their lives, leaving their futures open to interpretation.