A Blue Moon (ブルームーン,Burū Mūn?) occurs when two full moons occur in a month, on the second full moon, a night only once in several years. The magic of a blue moon has the power to reveal many secrets.
The entrance to the Blue Moon Abyss can only be seen on the night of a Blue Moon. The apparition in the abyss has knowledge of all things in the past, present, and future, which it may reveal to those who can appease it.