Koji Watanabe, also credited as Kouji Watanabe or Kozy Watanabe, is a Japanese creator known for his work as an original concept developer, writer, and manga author within the anime and digital media industries. He is most notably recognized as the original creator behind the science fiction franchise Platonic Chain, which began as an animated project before being adapted into a manga series. Watanabe was born on October 4, 1962, and is a graduate of the First Literature Department of Waseda University. His professional background is diverse, including experience as a member of a theater company, a musician, a copywriter, and a proposal writer for the film company Toho before he entered the computer game industry in the late 1980s. He is also the president of GTV, a company specializing in game and video software production.

The most prominent work associated with Watanabe is Platonic Chain. The original story was developed for an animated production by ACiD Inc., a company that utilized full 3D computer graphics to create a Japanese-style animation. The narrative, written by Watanabe, focuses on the lives of teenage girls in a futuristic setting where they possess broadband mobile phones. The initial animation was a short film showcased with a runtime of approximately four minutes, and its production employed various software including 3D Studio Max and Adobe After Effects. Following the anime, Watanabe is credited as the original creator and author of the Platonic Chain manga, which was published from April 2004 to June 2006, spanning five volumes. His name appears on the manga as Kouji Watanabe, and he is also listed as the writer for the source material.

Beyond his work on Platonic Chain, Watanabe has maintained a career deeply intertwined with digital media and content creation. After launching a monthly video game information magazine called GTV in 1988, he began serializing a novel titled 1999-nen no Game Kids in Weekly Famitsu. His creative activities extend to writing and developing serialized electronic novels and serving as a lecturer at Waseda University Graduate School. In a more recent capacity, a creator listed as Kouji Watanabe is credited as an animation director for the television series Meiji Gekken: 1874, which aired in 2024, suggesting an ongoing involvement in anime production beyond his original creator roles.