The series takes place in the futuristic, fictional Japanese town of Sugomori City. While the city appears to be normal, in reality, it was created to test a large-scale experiment known as the “Kizna System”. The ideal goal of the currently incomplete Kizna System is to create world peace by connecting people through shared pain and suffering. All those who are connected to the system are called “Kiznaivers”. If a single Kiznaiver experiences pain, either emotional or physical, the system distributes it among the other Kiznaivers.
A few days before the start of summer vacation, a mysterious and seemingly emotionless girl, Noriko Sonozaki, tells high school student, Katsuhira Agata, that he has been selected to become a Kiznaiver, alongside several of his classmates. This allows Katsuhira to share his pain and build bonds with his classmates, whose lives and personalities each differ from his own. This leads to serious implications as Katsuhira’s classmates attempt to shoulder each other’s pain and Noriko assigns them on various missions.