After creating five specimens, Shiro's final target is his beloved son, Itaru. Despite the memories with Itaru, Shiro only sees his son as a butterfly. Shiro makes up his mind to create his last specimen. At last, the report named "Human Specimen by Shiro Sakaki" seems to have ended. However, the letters in the report start to get distorted, and the story shifts to a new perspective.

Anna seemed proud, but she longed for a successor while looking at her mother, in the spotlight for her art book. After the art camp is canceled, Anna invites the boys to the mountain house. She insists she made the Human Specimen. Shiro understands Itaru's hopes to become his father's specimen. The truth of Itaru's death and the mystery of Anna's confession will be unraveled.