Often paired with writing veteran Hiroshi Kashiwabara, Wataru Mimura had a career largely focused around Toho's Godzilla productions in the 1990's and for their Millennium series run. Graduating from Japan's College University for the Arts, Mimura hit his first big break by winning a Sanrio Screenwriter Award in 1982 which led to work in the later part of the decade doing a few theatrical films such as Shochiku's Green Boy. However, his career started to stall in the early 1990's, stuck doing OV (Original Video, known as direct to video) work for Toei.

Mimura's next role would end up defining his career, as he was selected to script Godzilla vs. Mechagodzilla II (1993). Even before the film could become a box office hit, Toho followed up by awarding Mimura the job of writing Toho's Yamato Takeru (1994) and the film's sequel, which was never made. He ended up writing Staff Tokyo's Bad Guy Beach instead in 1995 before his career once more stalled.

In 1999, when Toho wanted to reboot the Godzilla franchise, they turned to Mimura hoping to work box office magic as he did in 1993. The resulting film, Godzilla 2000: Millennium (1999), ended up doing mild business during its theatrical run, but Mimura became Toho's go-to writer for the remainder of the Millennium series, as he helped script four out of the six films, including a joint screenplay for Godzilla: Final Wars (2004) with then Toho president Shogo Tomiyama.