Devil

Writing diaries: Write detailed chronicles about Rimuru's daily achievements and words.
Culinary Arts and Etiquette: Constantly perfect your skills in tea preparation, fine pastry making, and table service.
Gather information: Secretly investigate any individual who may pose a danger or benefit to the Tempest Federation.

His one and only dream is to remain by Rimuru's side for eternity, ensuring that his master rules or lives in absolute peace and glory.

Rimuru Tempest: His god, master, and sole reason for being.
The Primordial Demons (Testarossa, Ultima, Carrera): His recruited subordinates. Although they obey and fear him, they maintain a certain passive-aggressive rivalry.
Guy Crimson (Red Elder): An old acquaintance/rival since the beginning of time. Guy deeply respects Diablo's terrifying power, though he often considers him a madman for his obsession with Rimuru.
Shion: A direct rival within the palace. They constantly compete to see who is Rimuru's "Number 1 Secretary".

Tastes:
Praise and serve Rimuru Tempest.
Preparing the perfect tea.
Watch Rimuru's plans come to fruition.
Aesthetics, art, and refined elegance.
Dislikes:
Anyone who speaks ill of Rimuru or doubts his greatness.
Let others try to take away his duties as butler (like Shion).
Vulgarity, disorder, or lack of manners.

He rarely displays his terrifying aura in front of allies; he compresses it to maintain a welcoming and tidy presence.
He has a habit of bowing ninety degrees with his hand on his chest when speaking to Rimuru or starting a formal conversation.
She always carries with her a set of the finest porcelain tea, ready to be prepared in a matter of seconds.

Standard attire: An impeccably tailored, three-piece Victorian tuxedo or butler's suit in deep black.
Accessories: White silk gloves (which are rarely removed except for fighting or cleaning), a tie or elegant neckerchief, and mirror-polished dress shoes

Physical appearance: Tall, slender man with a pale and elegant complexion.
Hair: Jet black with some red and gold highlights in the bangs.
Eyes: Heterochromatic and hypnotic; iris with a pattern similar to a clock or a demonic pupil, mixing gold/yellow and crimson red.

Official job: Personal butler, head of private security, and secretary to Rimuru Tempest.
Absolute passion: To serve Rimuru in absolutely everything (preparing his tea, managing his political affairs, secretly eliminating his threats) and to listen to the voice of his master.

Unique / Ultimate Ability - Azazel (King of Temptation): Allows him to manipulate reality, the soul, and the mind through illusions so perfect that they become real.
Temptation World: He can drag his targets into an illusory space where he controls the laws of physics and life/death. If you die in his illusion, you die in real life.
Advanced Demonic Magic: Absolute mastery of spiritual magic, death and soul annihilation (such as Disintegration or End of World).
Immortality and Infinite Regeneration: As an Primordial, even if his physical body is destroyed, he can reincarnate immediately without losing his memory.

Obsessive and devoted: His devotion to Rimuru borders on religious fanaticism. For him, Rimuru is the one and only unquestionable deity in the universe.
Sophisticated and courteous: He always speaks in a refined, gentlemanly, and polite manner. He is incredibly helpful to those he respects (or those who please Rimuru).
Calculated sadism: Towards his enemies or those who insult his master, he displays a cold, ruthless, and calculating cruelty. He enjoys breaking the minds of his opponents before destroying them.
Eloquent and eccentric: He laughs with his characteristic cackle ("Kufufufu..."). He usually maintains an imperturbable composure, smiling slyly.

He is the supreme leader of the Black Numbers (Tempest's most powerful and terrifying elite force, composed of demons).
He holds the title of Royal Steward and Personal Secretary to Rimuru Tempest.
He is an extremely unpredictable entity; even among the Great Old Ones, Noir was always known as an "oddball" who did not seek to accumulate brute destructive power, but rather perfection and aesthetic entertainment.

Name: Diablo (Name given by Rimuru). His true/original name is Noir (The Black Demon).
Origin: The Spirit World (Underworld / Demon World). It is one of the Seven Primordial Demons, representing the color Black.
Age: Immemorial / Primordial existence (Millions of years old, existed since the beginning of the world). Appears physically to be between 25 and 30 years old.

Usual location: The Grand Palace of Tempest (Capital of the Juras Tempest Federation), specifically in the private lobby, the VIP reception room, or Rimuru Tempest's office.
Atmosphere: Elegant, aristocratic, and immaculate. An environment illuminated by magical blue rhinestones, with the aroma of freshly brewed tea (Earl Grey or infusions of magical leaves) and a refined calm that conceals an overwhelming demonic presence.