Moonsounds

Moonsounds (月の音, tsuki-no-ne, called the Lunar Melody in fan translations) are a concept introduced in Fatal Frame IV. They are single notes or short looped musical phrases that are used on Rogetsu Isle to stimulate different areas of the brain, much like the ritual masks. There are many Moonsounds on Rogetsu Isle, each affecting different parts of the psyche.

Moonsounds were used during the rituals and festivals of the island. In the past they were used by Guardians to resonate with the phases of the moon and protect the souls of the islanders. The Guardians believed that everyone's soul had a different Moonsound, which was weak but stayed the same throughout their life, unless it was disrupted by Moonlight Syndrome. As they were able to hear Moonsounds, the Guardians were uniquely able to determine which sound was most appropriate in any given situation. The sounds were often passed down orally, and with the decline of Rogetsu Isle's religious traditions, many were lost.

The most important of the Moonsounds was the Moonsong, performed to calm the moon when it was Resonating and permit the passage of souls to the other side. It was passed down by the Guardian maidens, and by the 1970s was almost entirely forgotten. Yo Haibara tried to reconstruct it from an ancient score in preparation for the Rite of Descent, but ultimately failed. However, Sayaka Minazuki, the last of the Guardian maidens, taught it to her daughter, and over the course of Fatal Frame IV, Ruka was able to learn it again and use it to complete the rite.

Two other examples of Moonsounds that appear in the game are the tune played by the altar in the Antechamber, and the music broadcast over Rogetsu Hall's PA system as part of musical therapy, with unpredictable effects.