|Occupation||Hiiragi Academy Chairman|
|Relatives||Arisu Hiiragi (cousin)|
|Manga Debut||Chapter 1 (hidden)|
|Anime Debut||Episode 2|
|Japanese Voice Actor||Suzuko Mimori|
|English Voice Actor||Jad Saxton|
Koyomi Hiiragi (柊 暦 Hiiragi Koyomi) is the Chairman of Hiiragi Private Academy in Denpa Kyoushi who scouted Junichirou Kagami to teach at her school due to his unconventional methods that he has bestowed upon her the nickname of "Options."
Koyomi is a very pale-skinned girl with straight mid-length white hair and purple eyes.
She is usually shown in the school uniform which is a short blue dress with long puffed sleeves and white cuffs, a white sailor collar and a small pink bow in the centre of the bodice. Her shoes are plain brown accompanied by knee-high socks. She is also always shown holding a white fan. Her eyes are a dark pink.
The chairman of the Hiiragi Academy private school. Koyomi finds Japan to be too boring by her standards, and wishes to transform the country into a more amusing place. She scouts Junichirou during his work at Higashi Shinmei High, impressed by his teaching methods, and decides to hire him to work as a teacher at Hiiragi Academy.
Since then, Koyomi always supports Junichirou’s schemes when they pique her interest, no matter how absurd they appear to be. She occasionally sends him, and the Ichou students Junichirou’s bonded with, to training-camps and whatnot to bring out their ability, and backs Junichirou when the former decides to challenge Koyomi’s cousin, Hiiragi Arisu, for the seat of Hiiragi Academy’s principal.
- The name Koyomi means "calendar, almanac" (暦).
- Koyomi's surname Hiiragi means "holly" (柊).
- Koyomi's goal is to transform all of Japan, transforming it into an 'interesting country', starting with the students.