He graduated from Waseda University in 1972 and joined to Tatsunoko Production as a story creator and a screenwriter.
After leaving from Tatsunoko, he wrote several screenplays such as Captain Tsubasa, Dragon Ball and Saint Seiya of Toei Animation.
By 1987, young screenwriters such as Satoru Akahori, Hiroyuki Kawasaki, Katsuyuki Sumisawa, Keiko Nobumoto and Aya Matsui graduated from Koyama's school.
Koyama authored a remake of Akira Toriyama's Soldier of Savings Cashman manga, that was illustrated by Katsuyoshi Nakatsuru and serialized in V Jump from June 1997 to December 1998.
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