Koichi Shidou

Koichi Shidou is the main antagonist of the manga/anime series Highschool of the Dead. He is a former teacher at Fujimi High School and the archenemy of Rei Miyamoto. A sociopath who only cares about his own survival, Shidou is the most persistent enemy to the group apart from "Them".

He is voiced by Kissho Taniyama in the Japanese version o the anime and Illich Guardiola in the English version.

Overview
Since "Them" are simply mindless monsters and not truly contemptible, Shidou's sole purpose seems to be to function as a character for the audience to despise. Indeed, while nowhere near as much of a threat as "Them", he is undoubtedly more evil, as he is in full control of his actions but just doesn't care. He has made enemies out of several of the main cast; Rei despises him due to him holding her back a year, which indirectly caused her relationship with Takashi to fall apart. Saeko mentions his name with scorn and Kohta states that he used to allow bullies to beat Kohta up as he watched with glee. The only ones who are fooled by his act are his followers, and that's because they're too blinded by their fear and desperation to see him for the monster he really is.

After the Outbreak, he sets himself up as a cult leader, promoting sexual activity among the teenagers to make them loyal to him. He is also a Social Darwinist, as his first act was to kick a teenager in the face who begged him for help, saying that the new world for people as weak as him. However, he is also a total coward, as when Rei has him at her mercy, he breaks down and begs for his life, which Rei only grants upon deciding he isn't even worth killing.

Moral Event Horizon
Shido crosses this in his first scene, when he kills one of his students (by leaving him to be eaten by "Them") just because he begged him for help. As far as Rei's concerned, however, he crossed it before the series even started, when he forced Rei to repeat a year just to get back at her father for rightfully exposing his father's political corruption.