Hollow Night (虚ろの夜, Utsuro no Yoru) is a mysterious realm that manifests once a month. It is home to the Voids.
"Those who get their souls devoured by the Dark Shadows, will end up wandering eternally in a mysterious world.", is the rumor that's being told around the city.
Hollow Night appears every time on the night of full moon at a certain area. Those people who are within the area during the Hollow Night's appearance enter to the Void's realm. Normal people who end up getting caught in the Hollow Night usually become the Void's prey, only some awaken as In-Birth.
People outside the realm of Hollow Night cannot see what happens within. Likewise, the people within the Hollow Night cannot view what happens in the real world. All electrical devices are also rendered useless within the Hollow Night.
Abyss (深淵, Shin'en) is a thing that appears in the center of the Hollow Night. It's an infinite fountain of EXS that many In-Births try to reach in order to gain further powers. Hilda hints that beyond the Abyss person can reach the status of a Re-Birth.
Due to the endless amount of EXS it produces, it allows to Voids to materialize so that people can visually recognize them.
Hollow Night can be forcibly ended by destroying the Abyss.