Kōichi Shidō is the homeroom teacher of class 3-A at Fujimi High School and a major antagonist in the story. He initially presents himself as a respectable educator, but his true nature is deeply manipulative, sadistic, and egotistical. His background includes being the son of a politician, Ichirō Shidō, and this family connection shaped much of his resentment. After his mother died, his father revealed the existence of an illegitimate son and forced Kōichi to work in the family’s shady operations, which fueled his deep hatred for his father and his desire to destroy the Shidō family name. This bitterness extends to his interactions with others, as he uses his position as a teacher to exert control and exact personal grudges.

Personality-wise, Shidō is charismatic in a deceptive way, able to sway groups through persuasive speeches and a calculated outward calm. However, he is fundamentally cruel, cowardly when directly threatened, and willing to sacrifice anyone he deems weak. He believes that only the strong deserve to survive and uses the chaos of the zombie outbreak to eliminate those he considers burdens. His primary motivation is to seize power and establish himself as the unquestioned leader of a new order, essentially building a cult of followers who depend on him. He sees the young survivors as angels who will help him reshape the world.

In the story, Shidō first appears as the teacher leading a group of students in a bus evacuation from the school. He quickly reveals his true colors by deliberately abandoning a student with a sprained ankle, kicking him back toward the pursuing zombies, and then delivering a speech about the importance of eliminating the weak. This action causes Rei Miyamoto and Takashi Komuro to leave the group. Later, Shidō gathers a following of students who are brainwashed into obedience through a combination of fear, intimidation, and twisted ideology. He manipulates them into ejecting anyone who shows doubt or concern for family, and he allows his followers to indulge in any behavior during “free time,” including orgies, mimicking cult-like control tactics. He eventually leads his group to the Takagi estate, where they are driven away. During an electromagnetic pulse event, his bus crashes into a barrier, inadvertently opening the way for a horde of the undead. He survives and later appears at the elementary school where the main group’s evacuation is set to take place, implying his continued threat.

Key relationships include his adversarial connection with Rei Miyamoto, who despises him because he caused her to be held back a year at school as revenge against her father, a police officer who had investigated his own father. Saeko Busujima also reacts with visible disgust at his name, and Kōhta Hirano once threatened him with a nail gun, implying that Shidō allowed bullies to beat him and watched with pleasure. Shidō’s followers are tools rather than allies; he keeps them in line through intimidation and the promise of a new world order. His development is mostly static, as he remains consistently manipulative and power-hungry, but his exposure as a fraud and his eventual desperation highlight his inability to cope without an audience.

Notable abilities are not physical; Shidō possesses no combat skills or special training. His strengths lie in rhetoric, psychological manipulation, and a talent for exploiting fear and uncertainty to gain followers. He is an adept public speaker and knows how to present himself as a calm authority figure while hiding his sadistic cruelty. His cowardice emerges when he is personally threatened, such as when he was briefly terrified by a nail gun aimed at his head or when Rei pointed a bayonet at him. Despite this, he is relentless in pursuing his own survival and ambition.