Hideyuki Saida

The anime's setting is a fictional Japanese city named Sugomori City. One day, Noriko Sonosaki tells her classmate Katsuhira Agata, "You have been selected to be a Kiznaiver." The Kizuna System, which allows Katsuhira to share his wounds, connects him to the classmates whose lives and personalities completely differ from his. The Kizuna System is an incomplete system for the implementation of world peace that connects people through wounds. All those who are connected to this system are called Kiznaivers. When one Kiznaiver is wounded, the system divides and transmits the wound among the other Kiznaivers. Sugomori City is built on reclaimed land, but as the years go by, the city's population is decreasing. The story is set in this town where Katsuhira and the others live.

As a child, Masamune Makabe once suffered greatly at the hands of a wealthy and beautiful girl named Aki Adagaki, who nicknamed him "Piggy" due to his chubby appearance. Seeking revenge against his tormentor, Masamune works hard to improve himself and returns as an incredibly handsome, albeit narcissistic, high school student. When he encounters Aki once again, he is prepared to exact vengeance. With the aid of the rich girl's maid, Yoshino Koiwai, Masamune slowly begins to build his relationship with Aki, intending to break her heart when the time is right. However, as his friendship with Aki begins to grow, Masamune starts to question the objectives of his devious plans, and if bringing them to fruition is what his heart truly desires.

The story centers around class 1-7 of Tennomifune Academy, where all the students with "bad karma" or misfortune seem to have been gathered. Hibari, a student in this class, meets the unlucky Hanako and the perennially unhealthy Botan on her first day of school, and together they try to find a way to turn their school life into a happy one.