“If no one remembers it, does that mean it never happened?”

Rogetsu Kagura is a festival held once every ten years on Rogetsu Isle in southern Japan. During the festival, five girls mysteriously disappeared. The girls were rescued by a detective, but all of their memories were lost.

One of the girls that disappeared mysteriously, Ruka Mizunaki, had a faint memory of a single melody…

- Girls playing instruments surrounded by masked people, and a masked woman dancing in the moonlight as though possessed. -

The melody repeats and hastens ... and then the memory ends abruptly. What happened that day...? Ruka has lived with that thought in her mind ever since. Ten years later, two of the girls that mysteriously disappeared were killed one after another. They were found with their faces covered, in a tragic demeanor. Determined to solve the mystery of their friends' deaths, the remaining girls, Misaki and Madoka, agree to travel to Rogetsu Isle.

Ruka decides to follow them to the island. Will they find out what lies beyond their lost memories?