Hiretsuna Josei

Hiretsuna Josei ( 卑劣な ・ 女性 ) is the teacher of Gakkō. Only the name is known, and doesn't appear or talk. The gender is also unknown.

Trivia

 * The first name "Hiretsuna" ( 卑劣な) means "Sneaky" in Japanese. It references how the teacher is "sneaky" for catching Ijime and his partners.
 * The last name "Josei" ( 女性 ) means "Lady" in Japanese. It's possible Hiretsuna is a female, but no one knows for sure.