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 aren't the same; anyone who tries to contact Him must go through a special ritual and a trial that involves a strange metaphysical puzzle.

History
1000 of years ago, Him made "The Promise" with Julius Ratri that demons shall no longer hunt humans, in exchange for Julius and his descendants to be forever stuck in an eternal cycle to oversee the Promise. After a certain time period, the demons celebrate and offer their prayers to Him. This feast is called the Tifari and involves offering only the best meal to Him.

Appearance
He has a small, rather child-like appearance. He's dressed in somewhat royal garments along with a cloak. His head consists of a skull with large horns. In the middle, He has one eye surrounded by three star-like markings.

He is also able to take on a more humanoid and adult appearance.

Personality
He possesses a somewhat playfully twisted nature and enjoys toying with humans. This is demonstrated by the fact that when Emma and Ray made their ways to "The Seven Walls" to meet Him, He put them trough several trials which left them in despair, confusion, and fear of the unknown. When Emma first meets Him, He appears to be extremely calm, laid-back, knowledgeable, somewhat friendly, and not hostile. Such as when Emma expressed her desire to free all the cattle children, He responded with a simple "okay", which shocked even Emma. However, He still gets serious and has his own demands. If He is to grant someones' wish, He demands the exact kind of compensation and will not accept any kind of rejection. For instance, When the Demon queen wanted to control the human meat supply to always be above the people, He demanded that the highest quality meat is given to Him to make a point of His superiority. And when Julius Ratri betrayed his friends so that he could end the war and finally live in peace, He decided that Julius and his descendants will be in charge of keeping the human side of the deal and collaborate with the Demons forever, so that he can never escape 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 here, 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 her 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, Him 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".