Ōji Hiroi is a Japanese author and video game developer born on February 8, 1954, whose real name is Teruhisa Hiroi. He is a prominent figure in the industry, recognized for creating major role-playing video game franchises and for his extensive work in anime and manga as an original creator.

One of Hiroi's most significant contributions to the mecha anime genre is the television series Madō King Granzort, which aired from April 1989 to March 1990. Produced by Sunrise, the series was created and directed by Hiroi, with Shūji Iuchi handling the screenplay. The story is set in the year 2100, fifty years after a mysterious moonquake terraformed the moon, making it habitable. A young boy named Daichi is chosen to become a Madō Warrior, using a magic gun to summon the giant robot Granzort to battle the evil Jadou Clan. The franchise expanded into multiple original video animations, including Madō King Granzort: The Last Magical War, Madō King Granzort: Non-Stop Rabi, and Madō King Granzort: An Adventure Story. The series is noted for its use of Kabbalistic and gnostic terminology, distinguishing it from similar productions of its era.

In the 2010s, Hiroi created the multimedia franchise Between the Sky and Sea, owned by the company ForwardWorks. The project began as a smartphone game released for Android and iOS on September 28, 2017. A manga adaptation written by Hiroi and ForwardWorks, with illustrations by Bekkourico, was serialized in ASCII Media Works' Dengeki Daioh magazine from September 2017 to November 2018, later compiled into two volumes. An anime television series adaptation produced by TMS Entertainment aired from October to December 2018, with Hiroi credited as the original creator of the franchise. The story follows a group of young girls who become space fishermen, battling in a unique science fiction setting.

Throughout his career, Hiroi has demonstrated a pattern of working across multiple media platforms simultaneously, often originating a concept as a video game or manga before expanding it into an anime series. His work on Madō King Granzort places him within the late 1980s golden age of mecha anime produced by Sunrise, a studio known for iconic franchises. His later work on Between the Sky and Sea shows his continued activity in the industry into the late 2010s, adapting to the rise of mobile gaming as a starting point for new intellectual properties.