Fifth-grader Masaru endures relentless cruelty at school, where he is bullied and publicly shamed online, and at home, where his own mother abuses him. Trapped in an unbearably hostile environment, he has no one to turn to. Then a mysterious, seemingly cute creature named Kyu-chan appears before him. At first, Kyu-chan seems like a comforting presence, but its true nature is far darker: it is a mad being born from Masaru's accumulated hatred and rage. Responding to Masaru's anger, Kyu-chan begins to mercilessly slaughter those who torment him. As the killings escalate, the story explores the psychological horror of a child's repressed fury given monstrous form. The narrative follows Masaru's descent into complicity and the escalating violence that blurs the line between victim and perpetrator. The setting remains grounded in Masaru's school and home, making the supernatural intrusion all the more jarring. The arc builds from the initial wish-fulfillment of revenge into a grim examination of the consequences of unchecked hatred.