Rasen (らせん, lit. Spiral) is a sequel to the movie Ring. It is directed by Jōji Iida, and, as with the first movie, is based on the novel Spiral by Kōji Suzuki.
Ring and its sequel Rasen 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; Rasen was written and directed by Jōji 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."
Takahashi and Nakata were later recruited to produce another sequel, Ring 2, which replaced Rasen as the sequel to Ring, having taken a different and original storyline from Suzuki's book.
Read more about Rasen: Plot, The "Forgotten Sequel"