The unique horror of biology! Yuukinuma in Sakura City is an artificial lake with its locks kept closed for a long time to prevent floods. As the flow of water stagnates and many creatures die, some species evolve to live. It was the spine of the human body, and it was to raise an embryo (embryo)! A horde of invertebrates attacks a peaceful student life! Nuko Nura, a girl who attends prefectural Shomon High School in Sakura, is a girl who likes insects and belongs to the Biology Department. One day, Kashiko gets stuck in the forest with a mysterious bug behind her neck.