Day and Night

The Day and Night (昼と夜) is an alternate dimension in which can be found.

Appearance
The Day and Night is a seemingly-infinite void divided by a horizon into a dark, night-like part and a bright, day-like part. The physics of the dimension behave strangely, with fish swimming in the air that a human can breathe and the floor creating water-like ripple effects while Emma walks on the surface of the Night portion. There appear to be structures in the far distance.

Demon cultural/religious significance
Being the residence of the godlike figure, the Day and Night is of much religious significance to the demons. Shrines like the Cuvitidala were created by the demons to view the Day and Night, however, these shrines were abandoned. The reason for the shrines' abandonment is officially unstated, but it could be in connection to the fact that, as stated by Sonju, demons have strayed from past religiousness in recent times due to influence by the previous king. Other places built with the Day and Night in mind were the demon temples that Emma and her friends visited, which depict art of the Day and Night on their ceilings, which is referenced later on by Ray.

According to Ray, many demons have tried to visit this place, but have failed. The Seven Walls has been observed by Emma to appear in art form of religious demon buildings, such as temples.

Cuvitidala
The easiest known entryway to the Day and Night is through the Cuvitidala. However, it is not the "correct" entryway, but only a vision, and upon entering, Emma is prompted by Him to go to the proper entrance.

Seven Walls
The proper entrance, the Seven Walls is much more challenging. Only two individuals, Julius Ratri and Emma, are known to have successfully made it to the Demon King and back through the Seven Walls.

Emma
Emma visits the Day and Night on two occasions, once through each entrance.

Julius Ratri
Julius Ratri entered the Day and Night in order to forge the original Promise.

The Demon King
The Demon King is the most notable inhabitant and the reason most, Emma included, seek to come to the Day and Night.

The Dragon of Cuvitidala
Spoken of in legends, the Cuvitidala Dragon is often seen alongside the Demon King. It does little but fly around and has no clear role as of yet.

Fish
Odd, fish-like fauna inhabit the Day and Night and are seen swimming around the Demon King.

Trivia

 * There is a secret passage Yverk and Julius used to reach Day and Night smoothly. In the current era, only the Queen and Yverk know about it. (Back at the time when Julius crossed, Geelan also knew that those people knew of a secret passage.)