Primordial

Primordials (原初の悪魔) also known as Progenitors or Primals, are the oldest and most extraordinarily powerful Daemons. According to Leon Cromwell, each of them is referred to by their signature colors rather than an actual name.

These "substitute names" don't count as their actual names in the true sense of being a named monster:
 * Purple Primordial Violet (Ultima)
 * White Primordial Blanc (Testarossa)
 * Yellow Primordial Jaune (Carrera)
 * Black Primordial Noir (Diablo)
 * Green Primordial Vert (Misery)
 * Blue Primordial Bleu (Rain)
 * Red Primordial Rouge (Guy Crimson)

Appearance
Black: Wears a full butler attire with white gloves. He has black hair with a strand of red in the front.

Red: Has flowing crimson red hair and eyes.

'Blue': Wears a deep-red maid outfit and has short blue hair and eyes.

'Green': Wears a deep-red maid outfit and has long, curly green hair and eyes.

White: Has silver hair, snow-white skin, and red eyes.

Violet: Has purple hair with a ponytail on the side and yellow eyes.

Yellow: Has short blonde hair and blue eyes.

Personality
According to Leon Cromwell, they are heretical and often troublesome because they fight using technique and wits instead of raw and sheer power, unlike usual Daemons.

Black: Rouge often labels Noir and the daemons of this color as oddballs that seem to have different values towards things other daemons would consider common sense, such as the pursuit of power. After being summoned by Rimuru, Noir immediately requested that he would be able to serve him and remains intensely loyal.

Red: Is by far the proudest of the Primordial daemons, and the only one of them without a master, instead declaring himself the first Demon Lord. He has an overbearing personality and does not hesitate to coerce people with threats to do what he thinks is best.

Blue: While she may seem to be a composed beauty on the surface, Bleu does not like working and leaves most necessary tasks to Vert. She likes to complain about a lot of things, even in the heat of battle. She is loyal to Rouge.

Green: Bleu's fellow maid to Rouge, she likes to take her tasks very seriously and devotes her all to her master, even creating a cult with her at the center to aid Rouge's observations of humans.

Purple: Violet is the Primordial with the youngest appearance and enjoys being treated like a princess by her lieutenant demons. However, she also has a fondness for the pain of others. Loyal to Rimuru after being convinced (beaten up) by Noir.

White: An absolute beauty with a seemingly gentle personality but is one of the scariest daemons of all in terms of personality. She massacred an entire city and more for laying hands on a friend of hers as is recorded in the Lake Shore Dyed Scarlet Incident. After swearing loyalty to Rimuru, she gets involved with politics by manipulating other members of the Western states council through various sorts of coercion. A stereotypical demon offering temptations.

Yellow: Before being taken under Rimuru's wing, she had the hobby of firing off sporadic bursts of nuclear magic, normally in the general direction of El Dorado. She has seemingly calmed down since then, but is viewed as a menace by anyone who knew of her before.

Story
Noir was summoned by a woman, one of two members of Silver Wings, who begged him to take revenge on the Arch Daemon Orthos. Noir then hunted down Orthos, fulfilling his contract. In the process of doing that, he met Shizue Izawa and took note of her Anti-Magic Mask that not only blocked one of his attacks but also ended up erasing one of his arms instead. The mask made him very intrigued, so after the incident, he secretly continued observing Shizue until the mask lost its Space-Time attribute when the mask reached Rimuru. Ever since he tried intercepting any Daemon summoning spell performed by Rimuru to get summoned, but the first time Rimuru used it, Noir got one-upped by Beretta instead. But upon Rimuru's second use of Daemon summoning, Noir, as well as two Greater Daemon aides successfully managed to be summoned by Rimuru. Shortly afterwards, Rimuru granted Noir the name "Diablo."

Blanc was the Daemon of note in the Lake Shore Dyed Scarlet Incident. She possessed a young woman by the name of Blanche whom she befriended. Her kingdom had a pact with the Primordial Daemon to one day sacrifice the princess' body to the Demon as a physical body as long as she kept them safe from other warring nations. This pact was cemented by the crimson eyes of every woman born to the royal family. When the country was destroyed due to schemes of several traitors and the Eastern Empire, Blanche chose to kill herself, which gave Blanc the possession of her body and ownership of her Soul. Blanc then took revenge for her friend causing what would later be known as the "Lake Shore Dyed Scarlet Incident." Then, after a few years passed, Diablo persuaded her to meet Rimuru alongside Jaune and Violet. After meeting Rimuru for the first time, she chose to join Tempest and was granted the name "Testarossa" by Rimuru.

Trivia

 * The nickname of each Primordial is the French word for their respective colors.
 * Primordials were introduced with the Light Novel. This terminology didn't exist in the Web Novel version.
 * Naming a Primordial is risky unless the namer is a Demon Lord (or on the level of one as Rimuru would have been incapable of naming Diablo before becoming a True Demon Lord) or has a surplus of souls to convert into magical energy.
 * Upon reaching a certain threshold of power, daemons are assigned a color that matches one of the Primordials based on their personality. All daemons of a certain color share the basic personalitiy traits of their progenitor and while they might express these traits in different ways, their demeanor and mindset are always a match for their progenitor.
 * For example Beretta, like Diablo, is polite, reserved, and affable while valuing things beyond strength and having a passion for learning or experiencing new things. Like Diablo, he is absolutely ruthless and unfeeling towards his enemies and can casually eliminate them without ever dropping his polite and affable demeanor.
 * Another example of this is Orthos, who was noted to possess the same prideful, cunning and manipulative disposition as his progenitor, Guy Crimson. This is seen where he showcased enough intelligence and cunning to root himself into human society and obtain his own personal kingdom and create extensive plans in order to further strengthen himself with the majority of the world being oblivious to his machinations, all traits possessed by Guy, his primordial.
 * According to Misery, Testarossa and Diablo form a troublesome duo.
 * Ultima is the shortest of the Primordials.
 * Each of the Primordials named by Rimuru is named after a supercar - the Lamborghini Diablo, Ferrari Testarossa, Ultima GTR, and Porsche Carrera GT.
 * As of the events of The Abyss Unleashed all of the Primordials have evolved into Devil Lords.
 * As of Volume 20, they’re also the only known Daemons to have evolved into Devil Lords.

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