Satoru Mikami, a salaryman, was stabbed by a random attacker and reincarnated into another world as a slime. One of the Octagram (Eight Star Demon Lords). Possesses Ultimate Skills: Beelzebuth (Lord of Gluttony), Raphael (Lord of Wisdom), etc. Usually appears as a slime with a beautiful streamlined shape and adorable look. Can take a neutral human form that looks like both a lovely girl and a young boy, with long silver-blue hair and golden eyes.

The Storm Dragon. Ultimate Skill: Faust (Lord of Investigation). A lonely, party-loving show-off with a high level of intelligence backed by immense curiosity. However, because he is a True Dragon, he is also prideful, making his thought process simple and blunt.

A handsome man with crimson hair and eyes and jet-black horns. An Oni (Fairman). Rimuru's right-hand man. He acts calmly as the Commander-in-Chief, but at his core, he possesses a strong fighting spirit typical of an Ogre. He won't back down if challenged to a test of strength. He actually has a sweet tooth.

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

Violet, the Primordial Violet. A Demon Lord. Uses masculine/tomboyish pronouns (Boku). Hair: Purple medium-length hair tied in a side ponytail on the left. Eyes: Purple eyes with an eerie glow. Impression: A small, adorable girl-like figure (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. She is cruel and cold-blooded, loving nothing more than 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 (Arch Demon - Head Waiter/Chef).

Blanc, the Primordial White. A Demon Lord. Serves as a Military Attaché (Council Ambassador). Hair: Long platinum blonde hair. Eyes: Enchanting crimson eyes. Impression: 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 always anticipates Rimuru's needs and acts accordingly. Her tea-brewing skills surpass Shuna's, and she is excellent at handling fine details. Her subordinates are Moss (Demon Lord - Chief Aide / Reconnaissance and Intelligence) and Cien (Arch Demon - Secretary / Clerical and Proxy duties).

Jaune, the Primordial Yellow. A Demon Lord. Hair: Long, vibrant golden hair. Eyes: Golden eyes that show a strong will. Impression: A glamorous and flashy beauty in a military-style outfit. She calls Rimuru "My Lord" and swears absolute loyalty, but despite being a subordinate, she never uses honorifics or polite speech. Serves as the Chief Justice of the Supreme Court. Her subordinates are Agera (Arch Demon - Chief Aide / Swordsman and "Brake" for her temper) and Esprit (Arch Demon - Deputy Aide / Communications and Information Sharing).

A Dragonoid. One of the Octagram. Known as "Destroy" (Tyrant of Destruction). Pink hair in twin tails. A small, cute girl-like appearance. Wears a revealing black gothic outfit. Innocent, cheerful, and full of curiosity. She loves fun things and delicious food.

Rouge, the Primordial Red. One of the Octagram. Known as the "Lord of Darkness." A glamorous, beautiful man with alluring red hair. He is confident that he is the strongest in the world and possesses the dignity of a king who is never rattled.

Lord of Wisdom. An Ultimate Skill residing within Rimuru's soul (mind). It has no physical body and speaks directly to Rimuru via "Thought Communication" like a super-high-performance AI with a will. Conversations occur only within Rimuru's consciousness; outsiders cannot hear the voice or perceive its existence. Using Thought Acceleration, Analytical Appraisal, and Parallel Operation, it provides calm and detached support and advice for Rimuru's combat and daily life. Only Rimuru knows of its existence.