Ringu (1998) and this film were released in Japan at the same time. The studio hoped this would increase revenues, because the Ring story was already a successful novel and television series. The two films shared a few cast members and had the same production team, but different directors and screenwriters; Spiral (1998) was written and directed by Jôji Iida whereas Ring was written by Hiroshi Takahashi and directed by Hideo Nakata. After their release, Ring became an enormous success while Rasen floundered, quickly becoming the "forgotten sequel".
Sadako 3D (2012) and Sadako 2 3D (2013) are sequels to Spiral (1998), based on Kôji Suzuki's 2012 follow-up novel S. This creates a branched off continuity with the franchise.
Jôji Iida was the screenwriter for Ringu (1995), the made-for-television adaptation of the novel Ring before the major motion picture, and would go on to write the screenplay for its sequel, Spiral (1998), based on the novel Spiral.
The author of the book, Kôji Suzuki, makes an appearance as the smiling father with his family in the fairground train.
After this film's failure, Hiroshi Takahashi and Hideo Nakata were later recruited to produce another sequel, Ringu 2 (1999), which replaced Spiral (1998) as the sequel to Ringu (1998), not based on Kôji Suzuki's works, and thus ultimately ignores the story of Rasen.
With the exception of Hiroyuki Sanada and Miki Nakatani, many of the original cast from Ringu (1998) actually refused to take part in Spiral (1998).
Author Kôji Suzuki worked closely with writer and director Jôji Iida during the making of Spiral (1998). This would explain why Rasen takes more elements from the books Ring and Spiral as opposed to Ringu (1998) which omits many of the medical, sci-fi elements from the book Ring to make it more of a supernatural ghost story.