Casus Puteus (ケェス・ピュトス Keisu Pyutosu, lit. "Abyss Descend" in Latin), or more commonly known as Hell Fall (奈落堕とし Naraku Otoshi), is a powerful spell used by Lieselotte Werckmeister to open the gate to the underworld. Upon completion, the spell will flood the world with Larva energy, wiping everything of Aether origin, living things or souls alike, off the face of the planet. In other words, this spell enables Lieselotte to destroy the world and re-create it anew.
This spell was cast inside Lieselotte's Specialized Bounded Field, Phantasmagoria.
In 1945, Liesette succeeded in activating Hell Fall at Ayamegaoka, Japan. However, after a fierce battle with the apostles of Index, the VoidStone in her body, which also served as the energy source of Hell Fall, was split apart by Georgius of the Rainbow and thrown into seven different dimensions. Consequently, Red Night became an in-between dimension that linked the seven mentioned dimensions with each other. Nevertheless, the giant door to the underworld that Lieselotte opened could not be undone. Therefore, the apostles of Index used their own lives to erect six crystal towers to prevent the portal from growing any bigger.
Originally, the Hell Fall changes the area of effect by turning it to red and materializes dark energies into solid creatures. However, after the battle in 1945, Georgius' seal detached the Specialized Bounded Field from the real world, creating an alternate crimson dimension, which was dubbed Red Night (赤い夜 Akai Yoru) later in the series. Inside Red Night, time flows much more slowly and whatever happens in this dimension does not affect the real world, at least until the spell is completed.
In addition to the blood-red space is the black moon that hovers in the sky. In fact, this "moon" is not the real moon but the gate to the underworld, which will bring forth calamity should the spell reaches its peak. Because of this, its size is several times bigger compare to the true moon and is located directly above the crystal altar.
- Main article: Astral Temple
Altering the Shin-Ayame Landmark Tower is a crystal altar with six towers. This is the one of the two things not originally included in the Red night but a consequence of the battle that took place in 1945. The altar is a base of the Black Knights, which serves both to imprison Lieselotte and to stop the black moon from growing any bigger.
- Main article: Larvae
Resides in the Red Night are numerous black squiggly creatures, which were called Larvae (闇精霊 Raruba) by the protagonists of Sin, Damnation and the Atonement Girl arc. They are, in fact, the dark energy that used to cover the entire Ayamegaoka, given forms by the negative thoughts and feelings of people in the real world. They are the exact opposite of Kukuri's Abraxas, as they are the manifestation of Larva, the sixth element of void and darkness while Abraxas is the manifestation of Aether, the fifth element that encompasses the canonical 4 and represents light. Every time a Black Knight is defeated, the power to suppress Hell Fall weakens, and the Larvae will evolve, changing both their forms and powers.
- Main article: Black Knights
Fighting off the Larvae inside Red Night are the Black Knights. They are, in fact, the Punishment Squad of saint Georgius from Index sent by the pope Johanna to Ayamegaoka in 1945. After the battle with Lieselotte, they lost their lives and were forced to use the Larvae' bodies as their own to continue the job of stopping Hell Fall. In the anime, however, the Black Knights' forms are the result of the spell they used to seal Lieselotte.
Maiden of the Crystal Palace
- Main article: Lisette Vertorre
Lisette is a girl trapped in the gigantic crystal protected by the Black Knights. She is, in fact, Lieselotte, the caster of Hell Fall and the only real resident of Red Night. After the battle in 1945, her powers and memories were stripped off and Lieselotte was reduced to Lisette, her human origin. Aside from her own name, Lisette Vertorre, she has no memories of her past. She is immortal and does not feel thirst or hunger, only loneliness and fear for the grotesque appearance of the Black Knights who surround her.
Red Night covers the entire Ayamegaoka in a radius of about 15 kilometers. While acting as the linking dimension, it does not affect humans or any other living creatures in any way. However, after the seven fragments of the VoidStone are gathered in Ayamegaoka, each in his/her own dimension, a reaction happens and the bearers of the fragments will be dragged inside Red Night.
The amount of time the fragment bearers can stay inside Red Night varies differently, and each time the Red Night breaks, a fragment bearer will not return to his/her original dimension. Instead, they will be transported into an overlapped reality, which is the result of Red Night's interference.
It should be noted that the apostles of Index are the ones present on Ayamegaoka at the time Hell Fall occurred. Therefore, they are permanently trapped inside Red Night, with the exception of Superbia, who can travel between Red Night and the real world easily.
- According to Misao, Georgius' group has been staying in Red Night for only 3 months, while in fact 64 years has passed. This makes one day inside Red Night is equal to approximately 260 days in the real world.
- In the 11eyes OVA, a twisted version of Red Night, called the Pink Night, occurred in the dimension that the protagonists were staying. In this "Night", everything considered supernatural are all messed up in various perverted ways.
- The towers surrounding the crystal altar has old Roman style in the game. In the anime however, they are also crystal.