Can be considered a sequel to the TV series "Ring: Final Chapter", since it mentions the cursed tape whose viewer will die in 13 days (and not the original seven, as the other adaptations), and Akiko Yada reprises her role as Mai Katano. However, it can also be viewed as a standalone work.
Although loosely based on the novel "Spiral" by Kôji Suzuki, it borrows elements from other books in the series, as "Ring" and "Loop" (which has never been fully adapted in any medium), and even foreshadows some events that would take place in Suzuki's later novel "S".