Kōichirō Yasunaga is a Japanese manga artist born on January 13, 1962, in Oita, Japan. He made his professional debut as a creator in the pages of Shōnen Sunday in 1980. Yasunaga is best known for his manga series Prefectural Earth Defense Force, which began serialization in Shōnen Sunday Zōkan in 1983. This work is a parody gag manga inspired by the tokusatsu series Ultraseven. The series was later adapted into an anime original video animation (OVA) released in 1986, with animation production by Studio Gallop and production by Shogakukan. The manga was published in four volumes by Shogakukan from 1984 to 1985, and the anime OVA was released on DVD in North America by ADV Films on April 18, 2006.

Yasunaga is also credited as the original creator for the live-action OAV Big Boobs Buster, released on April 25, 1990. For this project, he is listed as providing the original story, with a screenplay written by Hisashi Watanabe, who also directed the OAV. The work is a comedy with a plot centered on a high school student who becomes the "Big Boobs Buster".

His other known manga works include Kyonyū Hunter, Rikugun Nakano Yobikō, Kaitei Junrui Anchovie, Chō Kankaku Analman, Kaseijin Deka, Eichi Man, Ganjō Ningen Spartacus, Chōjin Totokarucho, Jitsuroku Jion Taiiku Daigaku, and MM Little Morning. Yasunaga’s body of work, particularly Prefectural Earth Defense Force, establishes him as a creator of comedic and parodic manga, often blending science fiction and tokusatsu elements with absurdist humor.