Him

Him (also mentioned as "The One") is seemingly the God of all Demons and the Demon World. He is often referred to as a deity. His actual name is not yet clear, but is mentioned in several instances and is pronounceable by humans.

He lives in a special dimension where the laws of time and physics do not apply; said to be located in a mysterious space with a dragon, anyone who tries to contact Him must go through a special ritual and trial that involves strange metaphysical puzzles.

History
His origins are unclear, but he is considered deity-like by the demons, and was the one capable of making Promises on their behalf.

1000 years ago, He made the deal with Julius Ratri that became known as the Promise; the demons and humans would be partitioned between two worlds, unable to access one another. The human world would be free of demon predation, and in exchange the demons would be allowed to farm the humans stranded on their world. The Ratri clan additionally were tasked with maintaining the promise, with Julius Ratri forced to stay in the Demon World. For the Demon's, He declared the Tiferi, a festival which would culminate in the very best of all humans who were farmed be offered to Him as tribute.

Appearance
He is small, with a child-like appearance. He' is dressed in regal clothing with a hood. His head consists of a skull with large horns. In the middle, He has one large eye surrounded by three star-like markings.

He is also able to take on a more humanoid and adult appearance, implying his form is a matter of choice than necessity.

Personality
While his full nature is unknown, he is shown to possess a playful, alien and possibly sadistic nature. While seemingly disinterested in devouring humans as a first response, he was the one who established the Promise and thus the system of Human farming, and shows neither remorse nor concern for the humans plight, or the mental suffering afflicted upon Emma and Ray as they passed through the Seven Walls and left them in despair, confusion, and fear of the unknown.

The exact motivations and need of Him are unknown, though his actions may simply be a method of entertaining himself. He is not hostile when meeting either Emma or Julius Ratri, but displayed seriousness when it came to exact his price and the requirements of his promises. Seemingly, all that is needed to cause him to allow a new Promise to be made is reaching him; when Emma expressed her desire to free all the cattle children, He responded with a simple "okay".

In contrast, in exchange for creating his Promise, He demands a specific payment that he will not reconsider. This price appears to be commensurate to the Promise itself; one must give up the thing that they most desire from the Promise. For the Demon Queen, it was the most valuable human meal of the year, to prove to her she will never be his superior, for Julius, who betrayed his friends to escape the Demons, he was forced to be the guardian of the Promise in the Demon World for the rest of his and his families lives, ensuring he could never be free of his pain and especially not his guilt.

Introduction Arc
Yverk is pleased by the information that Grace Field House's premium children, Emma, Ray and Norman, are able to be shipped out. He states how everything must be ready and perfect for the Tifari. The premium children shall be offered, as he evokes his prayers to Him.

Jailbreak Arc
When Emma and Norman talk to Krone and asked her about information, Krone questioned whether they know about Him. They were confused and she promised to tell them next time.

Promised Forest Arc
The children expressed their plans to break the Promise. Mujika says they'll make an enemy of The One but Sonju said that He was their enemy from the start.

Cuvitidala Arc
When Emma, Ray, Violet, Zack, Don and Gilda arrived at Cuvitidala, Emma noticed odd markings on the stones. After touching them, she is transported to another realm and has visions of the past. She also meets Him there. He is surprised by her appearance and tells her that there is nothing there, yet at the same time everything. Before Emma could confirm if He really was Him, He said, that it's time to play and sent her back to the demon world to the others. As Emma and the group left Cuvitidala, Him appeared behind them as he watched the children leave.

Seven Walls Arc
Emma wants to reforge the promise with Him and make a new one, so that humans and demons can finally live in peace. She and Ray perform the ritual to enter His realm. They end up in a strange world, where He is seemingly able to manipulate space and time. But it turns out that the realm is influenced by their conscious and subconscious minds. In this strange world they found a four-dimensional hypercube with a pitch-black spherical opening that looks like a black hole. Emma is sure that this object is the gate to reach Him. Emma and Ray grab their hands and decide to touch the black hole-like object.

After this, Ray is teleported back to the shelter while Emma meets Him in "the place of night and day". There Cuvitidala flies down and He emerges. He also shrank from a more humanoid form into his regular small appearance. He explains to Emma how Ray was unable to enter the place because his own mind was too centered around logic and he couldn't break free as Emma did, This is what makes Him remark to Emma (that she must be very delicious). Emma then asks Him to reforge the promise. He simply says "OK", much to her surprise. Nevertheless, He still requests a reward in exchange from Emma, just like 1000 years ago.

Trivia

 * In the manga, when the characters such as Yverk, Emma and Krone mentioned the demon, he is referred to by his name in the demon language, . In the anime, however, was referred to as "Him".