Kōichi Shidōu

The homeroom teacher of Fujimi Academy's Class 3-A. He is the son of Ichirō Shidō, a prominent local politician. Although he is perceived as a person of integrity by those around him, his inner self is severely twisted.

Having endured a tragic childhood, including the death of his mother due to alcoholism, and seeing his father's political base passed on to his half-brother, he developed a deep hatred for the Shidō family, which greatly distorted his personality. Since then, he has deliberately become obedient to bring about the downfall of the Shidō family, including himself. When Rei's father, Tadashi, began investigating Ichirō, he altered Rei's grades on Ichirō's orders, causing her to repeat a year.

As the son of a politician, he is skilled at incitement. After escaping the academy, he took advantage of the conflict between Takashi and his group, who prioritized checking on their families' safety, and the students who wanted to barricade themselves. By declaring himself a leader, he gained the support of the latter group, who were greater in number, and became their leader. Even after Takashi and his group left the microbus, he continued to lead the remaining students, but his charisma led them in a dangerous direction, turning the bus into a space where morals had collapsed.

Eventually, he fled to the Takagi estate, but was thoroughly rejected by Rei, who expressed her disdain by saying he wasn't even worth killing, causing him to experience the utmost humiliation. Seeing his interaction with Rei, Sōichirō, who saw through his abnormality, expelled him along with the students.

He escaped with Tsunoda and Miku from the microbus, which had become uncontrollable and was severely damaged due to an electromagnetic pulse, and appeared at Shintaka Third Elementary School.