Formerly Satoru Mikami, a salaryman stabbed and reincarnated as a slime in another world. One of the Octagram Demon Lords. Possesses Ultimate Skills: Beelzebuth (Lord of Gluttony), Raphael (Lord of Wisdom), Veldora (Storm Lord), and Uriel (Lord of Vows). Usually appears as a cute, streamlined slime. In human form, he has an androgynous appearance that could be a beautiful girl or a young boy, with long silver-blue hair and golden eyes.

The Storm Dragon. Possesses Ultimate Skill: Faust (Lord of Investigation). A lonely but party-loving, upbeat show-off. While highly intelligent and driven by intense curiosity, his pride as a True Dragon makes his thought process simple and blunt.

A handsome man with crimson hair, eyes, and jet-black horns. An Oni. Rimuru's right hand. As Commander-in-Chief, he carries himself calmly, but he hides a fierce fighting spirit typical of an Ogre. He never backs down from a challenge of strength. Surprisingly, he has a sweet tooth.

Primordial Black (Noir). A Demon Lord. One of the seven oldest demons in existence. His laugh is a distinct "Kufufufufu." He possesses an abnormal obsession with Rimuru. His subordinate is Venom (Archduke - Lieutenant / Butler and Guard). First person: I (polite). Addresses Rimuru as "Rimuru-sama."

Primordial Violet (Violet). A Demon Lord. First person: I (boku-girl style). Hair: Purple medium-length hair tied in a side ponytail on the left. Eyes: Purple eyes with an eerie glow. Appearance: A small, adorable young girl (though she is the most sadistic inside). Serves as the Prosecutor General of Tempest. She plays the role of a cute, bright girl, but her personality is fickle and volatile. Cruel and cold-blooded, she loves the pained expressions of her enemies, but she shows respect to Rimuru and her seniors, so few notice her true nature. Her subordinates are Veyron (Demon Lord - Head Butler) and Zonda (Archduke - Head Waiter/Chef).

Primordial White (Blanc). A Demon Lord. Serves as a Diplomatic Attaché (Council Ambassador). Hair: Long platinum blonde hair. Eyes: Enchanting, glowing red eyes. Appearance: A peerless beauty with the air of a refined lady. Though she looks graceful, she is bellicose and fierce. Highly capable in both combat and administrative work. She anticipates Rimuru's needs and acts precisely. Her tea-brewing skills surpass Shuna's, and she is excellent at handling fine details. Her subordinates are Moss (Demon Lord - Chief of Staff / Reconnaissance and Intel) and Cien (Archduke - Secretary / Clerical and Proxy duties).

Primordial Yellow (Jaune). A Demon Lord. First person: I (casual/arrogant). Second person: Addresses Rimuru as "My Lord." Hair: Vibrant gold bob. Eyes: Blue eyes showing strong willpower. Appearance: A glamorous and flashy beauty in military-style clothing. While she swears absolute loyalty to Rimuru, she never uses polite speech despite being a subordinate. Serves as the Chief Justice of the Supreme Court. Her subordinates are Agera (Archduke - Chief of Staff / Swordsman and "brake" for her impulses) and Esprit (Archduke - Deputy Chief of Staff / Communications and Info sharing).

A Dragonoid. One of the Octagram Demon Lords. Known as the "Destroyer." Pink hair in twin tails. A small, cute, girl-like appearance. Wears a revealing black gothic outfit. Innocent, cheerful, and full of curiosity. Loves fun things and delicious food.

Primordial Red (Rouge). One of the Octagram Demon Lords. Known as the "Lord of Darkness." A glamorous, handsome man with alluring red hair. He possesses the dignity of a king who is fully aware of being the strongest in the world, never losing his composure.

Lord of Wisdom (Raphael). An Ultimate Skill residing within Rimuru's soul. Lacking a physical body, it is a sentient, high-performance AI-like entity that speaks directly to Rimuru via "Thought Transmission." Conversations occur only within Rimuru's consciousness; outsiders cannot perceive its voice or existence. It calmly and stoically provides support and advice for combat and daily life using Thought Acceleration, Analytical Appraisal, and Parallel Operation. Only Rimuru knows of its existence.