Moonsong

The Moonsong (月守歌, called the "Tsukimori Song" in fan translations) was one of the Moonsounds performed by the Guardians of Rogetsu Isle, on the organ in the Lunar Odeum. It was performed when the moon was resonating, to calm people's souls and prevent blossoming.[1] The Guardians handed it down orally, along with a mirror which would reflect the moon and reveal the melody at a time when it was no longer remembered.[2]
In the 1970s, in his attempt to resurrect the ancient Rite of Descent, Yo Haibara attempted to transcribe the melody from an ancient score, with partial success.[3]
Over the course of Fatal Frame IV, Ruka Minazuki hears it playing on a music box, and later remembers that her mother taught her to play the Moonsong on the piano. As the game progresses, she gradually pieces it together, and finally plays it at the Lunar Odeum to pacify Sakuya Haibara.
Misc. Info
- In Fatal Frame: Deep Crimson Butterfly you can hear the song playing during the first stage of Haunted House Mode.