Zerozaki Soushiki no Ningen Shiken

Now that he’s a cool college student, our anti-hero Iichan thinks his crime-solving days are behind him. Cynical, sarcastic and minimally engaged in his studies, Iichan is much more interested in his own feelings of disaffection and isolation. But despite his resolve to remain aloof, he’s pulled into the narrative when he encounters and bonds with a serial killer named Hitoshi Zerozaki – a homicidal maniac with the soul of an artist whose talent is on display at the grisly scenes of his crimes. (Source: Kodansha USA)

Let's commence the Zerozaki, cha. The most crude and merciless demonic killers fight to the death. The Zerozaki Clan is a family of demonic killers, ranked third among the Killing Names. Zerozaki Kishishiki, the user of a bat covered in nails known as "Seamless Bias (Foolish Prayer)". One after another, elite Killing Names enter the field. What lies at the end of this deadly battle? The forefront of new youth entertainment is here! (Source: Kodansha, translated)

Iori is a high school girl who doesn't know what she wants to do with her future, and tends to run away from things. One day, she is attacked by strange dead-eyed people on her way to school, only to be saved by an equally mysterious long-haired man. Later that day, her friend at school, Jion, seems to fall under the same murderous influence. To her surprise, she finds herself capable of defending herself from his violent attack. Afterward, the long-haired man she met in the morning, Zerozaki Soushiki, arrives once more, this time to invite her to become his little sister. What has Iori become involved with, and will she be able to survive this change to her life?