This is the third VN in the Tiny Dungeon series (see: http://forums.fuwanovel.net/blog/46/entry-727-tiny-dungeon-black-and-white/ and http://forums.fuwanovel.net/blog/46/entry-747-tiny-dungeon-bless-of-dragon/ for the first two). This one is focused on Note Ruum.   Note Ruum's secret you will already know from Black and White (it is central to the drama near the end), but I will refrain from revealing it anyway. She is the First Princess of the Divine World, as well as being the 'Grand Luna'