Exetior The Arch-Demon.

Exetior is the primary antagonist and overarching antihero of the Sonic.exe: Nightmare Universe (abbreviated as NU) series by JaizKoys. He debuted as the titular main antagonist of Sonic.exe: Nightmare Beginning, as well as one of the three of Sally.exe: Continued Nightmare alongside Sark and Stich-Light. Exetior is the Chosen One of Chaos. He was originally an Elite Highest, but was transformed into an Arch-Demon due to his demonization awakening his gift from the Great Chaos. Because of his background and how others in his homeworld treated him, he is very prone to losing his composure and having outbursts of anger when agitated. Among Demons and mortals, he is seen by others as very calculating, charismatic and persuasive. His ferocious personality and reputation is well known among Demons across the universe.

Exetior possesses a degree of restraint compared to other demons due to having a code of honor. While in earlier games he was far more malicious and bloodthirsty, this changes after Sally.exe: Finished Nightmare, where he begins to learn what it truly means to save Mobius. Both Sonic and his victims are allowed to keep their individuality when demonized, with his servants each retaining the personality their former selves.

When Exetior was born to the all-powerful Highest race, he was blessed by the supreme being Chaos, which immediately created suspicion and concern among his entire race. Chaos' "gifts" would often lead to terrible events that caused the Highest to lose their iron grip on existence. This caused the other Highest to hate Exetior and treat him like a pest they should get rid of, but rather than choose to side with the rest of the public, the Highest leader All-Father saw potential in the young god and decided to make him a key Highest involved in the creation of new planets, stars and dimensions. Eventually, Exetior with the help of some other Highests would create a planet known as Mobius. It immediately caught Exetior's eye as he would begin to develop it even more.

Despite his newly found position among his society, the other Highest were still too bigoted from their fear of Chaos and never gave him the proper love he desired. Exetior took offense to this and decided to raise an army to overthrow their society and it's control on the universe as a whole, using his charisma and overwhelmingly powerful aura under the guise of an Arch-Demon to garner new followers. These new allies included the bloodthirsty Sharpness Demon Sark, the reclusive Wave Demon Negagen, and the mad scientist Rupter Demon Pervision. Unfortunately as the war between the Demons and Highests emerged, Exetior's side was crushed by the might of the Highest, being sent to rot in the Phantom Prison.

While he was locked up and stripped of his Highest authority, Exetior's conscious began to flood with feelings of intense rage. As he kept having violent anger outbursts, his power caused his Highest form to deteriorate and transform into something more sinister, completely becoming an Arch-Demon in the process. The intense amount of power his transformation exerted allowed him to break out of the Phantom Prison, to which he escaped and also freed other imprisoned demons that were crucial in his army.

As he hid across many different planets, dimensions and other places, the Highest would always manage to find him and erase his progress made. Eventually he would stumble across Mobius again, hiding within Sonic's body to mask his aura from them. Exetior was unable to completely take over Sonic's body because it was protected by a chained demon named Creep. He told Exetior that Sonic's strong will made it difficult for him to be possessed. However, if sonics friends and three main parts of his determination were destroyed (Tails, Knuckles and Eggman), it could potentially leave him powerless and possessable. Exetior agreed to this choice and temporarily possessed Sonic's body. He was successful and managed to kill and demonize Tails, Knuckles, and Eggman. He is now hunting Sally Acorn, Cream The Rabbit, and Amy Rose. Exetior has some sort of personal vendetta against Cream despite him admitting she is a good kid, the reasoning is unknown behind his dislike, even unknown to him.

He is over 10,000 years old. He is genderless, but prefers masculine pronouns. He has a weakness for quiet and obedient children. While not needing food, he prefers salty and sweet foods (likely due to inhabiting Sonic, who prefers chili dogs) His favorite food is fried fish. He is naïve around his circle of friends. He does not like to be referred to as "Lord".

Exetior has multiple demons working under him, such as Sark The Demon of Sharpness (arguably the most deranged demon, he possessed Sonic from another dimension and conquered that Sonic’s version of Mobius and enslaved all the women (all female Sonic characters) and killed all the men (all male Sonic characters)), Pervision The Demon of Gap (mad scientist and creator of multiple abomination hybrid creatures, he also created Jina), Negagen The Demon of Wave (Exetior’s apprentice and emotionless demon), and finally Jina (Exetior’s pseudo girlfriend, she flirts with Exetior and clearly likes him, he doesn’t admit it but he like her back).

Sally puts up a serious and stoic facade when at work, though that is not her true attitude. Sally, in reality, is much nicer and likes to spend time with her friends. She is stubborn, and does not easily believe those she is against. She really does not trust Exetior. Sally is a short, anthropomorphic chipmunk. Sally has brown fur with a light brown muzzle and torso as well as short, auburn hair, blue eyes, a short tail, and a short, open, light-blue vest and tall, dark blue boots with gray soles.

Cream has a sweet and understanding attitude, and she greatly admires Amy and Sally. She is also rather polite, referring to others as "Mr." or "Ms." frequently. She is hyperactive, and despite being young, she is greatly courageous. Cream, is a small and cream-furred anthropomorphic rabbit with cinnamon-brown eyes, a small brown nose, and a white muzzle. She has princeton orange markings around her eyes, on her head and at the tips of her long ears. She also has one long eyelash on each eye and a short and fluffy tail that sticks out of her dress, though it is not always visible. For attire, she wears a simple sleeveless vermilion dress with a white collar and a light blue cravat, white gloves with a gold cufflink on each cuff, white socks and vermilion and yellow slip-on shoes with gray soles. Her ears also have pink-colored canals and are usually swiveled back and flop behind her head.

Amy's personality is very different from canon. She is not obsessed with Sonic, and is much more independent and skilled. She is greatly protective of her friends and is quick to try and save them from harm. She has also shown herself to be selfless, helping people that she does not know several times. She is very polite, cute, adorable and always actually had feelings for Sonic, even when he was trapped ''inside'' of Exetior. Amy Rose is a short, pink furred anthropomorphic hedgehog. She has three short, yet upturned quills on the back of her head, a tuff of quills on her forehead, two conjoined eyeballs with black eyes, a short tail, and peach skin covering her muzzle, inner ears, and arms. She has small black nose, triangular ears on top of her head, and no back spines. She also had two medium-length eyelashes on each side of her eyes. Her standard attire is an green-ruffled or pleated skirt, a white shirt with a red heart in the middle, and purple sneakers with white stripes, white wrist-length gloves, and a red ribbon hairband.

Jina, due to being spliced from Sally, Cream and Amy, has a split personality where she exhibits traits of each girl. She can be careful and cold, playful and childlike or flirtatious and passionate. She’s also rather confident and cocky. Jina’s appearance doesn’t point to her being one species of mortal. This is due to her being made of multiple. On her head there is a odd/out of place melted jelly looking like thing. This is a result of the phantom ruby interacting with a demonized brain. Her eyes change colour depending on her emotions. Cheerful/playfull/funny = green, interested/calm = yellow, surprised = light yellow, angry = red, in love/flirting = pink, confident = blue, sadistic = reddish orange, serious/gloomy = grey and embarrassed/ashamed is light blue. She’s made of demonized mortals with demon blood added. She wears a red dress with a darker red belt and heeled boots with straps.