So I thought it was time for a break down of Fatal Frame 4 from what we know. Beyond the Camera len's translations

What about the name of the game? "The Mask of the Lunar Eclipse"? What significance does that bear?
The only reference I could find to an eclipse was the Shinto sun goddess "Amarterasu" who caused an eclipse by sealing a cave, from what I've read. Hurriedly, on the subject, the world was later saved by a sumo (which, whilst saying something for the bravery of the sumo, doesn't seem in keeping with the theme of the series).

What about masks?
The first thing that comes to mind are Japanese Noh Theatre masks. The noh performances are based on 6 groupings, possibly it could be used for 5 girls and an eclipse as the 6th grouping?
Although, the Noh theatre has routes in Buddhism, not Shinto (like I think the rest of the series is), so again, not in keeping with the vibe of it's predecessors.

Honestly I don't think I'll ever guess the story before I play it, but its fun to think about it and take wild guesses, and learn some Japanese folklore in the process.