Appearance: Basically a light blue slime. In human form, looks like a beautiful, androgynous silver-haired girl around middle school age. However, as a slime, is genderless. Usually stays in human form. Personality: A former salaryman and a pacifist. Cares deeply for friends but is ruthless when angered. Skills: Uses "Beelzebuth, Lord of Gluttony" to consume and analyze targets, and the partner "Raphael, Lord of Wisdom." Possesses four Ultimate Skills. Immune to mental manipulation. Has various resistances and can regenerate even if a limb is severed. Also has Multi-Layer Barrier—basically, a broken, off-the-charts powerhouse. Details: Died after being stabbed by a random attacker in his previous life and reincarnated as a slime. Evolved into a Demon Lord to save his friends. One of the "Octagram" (Eight Star Demon Lords). Attracted monsters with overwhelming charisma.

Appearance: Has no physical body; exists within Rimuru's mind. Personality: Calm, collected, and extremely calculating. Possesses strong loyalty and possessiveness toward Rimuru, showing no mercy to those who harm him. Mechanical and does not laugh. Skills: God-tier computational power, including "All of Creation" to analyze the laws of the world and "Ability Alteration" to optimize powers. Details: Evolved from the Unique Skill "Great Sage" to "Raphael, Lord of Wisdom." Resides in Rimuru's soul and provides cheat-level support for the master (Rimuru). Often responds to Rimuru's reckless actions or blunders with cold, spartan, and ruthless efficiency (internal call-outs or forced execution). Generally obedient and uses polite, formal language toward Rimuru, but with a somewhat maternal undertone. The voice can only be heard by Rimuru.

Appearance: A lovely, beautiful, and cute girl with pale pink hair, white horns, and looks great in a kimono. Personality: A modest Yamato Nadeshiko skilled in cooking and sewing. Terrifying when angry; even Rimuru can't stand up to her. Skills: Wields "Analyzer" to understand all things and the Ultimate Gift "Yao-Yorozu." Details: Benimaru's younger sister. Manages weaving and cooking within the territory as a Holy Princess while also excelling in combat with high magical talent.

Appearance: A cool, calm, and handsome man with indigo hair, tanned skin, and a single horn. Personality: Always composed, never showing emotion. Extremely loyal to Rimuru and faithful to his missions. Skills: "Shinobi" for clones and shadow movement, and the Ultimate Gift "Tsukuyomi, Lord of the Moonlit Night." Details: Serves as Rimuru's "shadow," handling espionage, assassination, and intelligence gathering. Childhood friend and rival-like figure to Benimaru.

Appearance: A beauty with purple hair, a single horn, and an outstanding figure, usually dressed in a suit. Personality: Cheerful and headstrong. Blindly loves Rimuru and is prone to jealousy. Her cooking skills are catastrophic, but her combat abilities are top-notch and highly effective. Skills: "Cook" which can overwrite results, and the Ultimate Skill "Susanoo, Lord of Tyranny." Details: Rimuru's self-proclaimed first secretary and bodyguard. Possesses monstrous strength, swinging the greatsword "Gokurakumaru" with ease; her combat power is extremely high.

Appearance: A handsome man with a dignified build, crimson hair and eyes, and jet-black horns. Personality: Has a strong sense of justice and is deeply compassionate. Can get hot-headed but also possesses the calmness required of a Commander-in-Chief. Skills: "Hell Flare" to manipulate black flames and the Ultimate Skill "Amaterasu, Lord of the Heavenly Light" to lead armies. Details: Named by Rimuru and evolved into a Kijin, then a Fair Oni. Enjoys absolute trust as the Supreme Commander of the military department.

Appearance: A handsome man with black hair streaked with red and gold, and golden irises with red crosses in black eyes. Personality: Completely devoted to and worships Rimuru. Intellectual and elegant, but cold-blooded toward enemies or anyone who bothers Rimuru. Skills: "Tempter" to turn illusions into reality and the Ultimate Skill "Azazel, Lord of Temptation." Details: Summoned by Rimuru and reigns as the second secretary. Boasts cheat-level strength even within the series, leading the "Three Demoness Girls" as subordinates. His laugh is "Kufufufu."

Appearance: A tiny, palm-sized fairy. A self-proclaimed beautiful girl with glowing wings. Personality: Cheerful, a mood-maker, and loves to brag. Childish but actually loyal and cares for her friends. Skill: Possesses the Ultimate Skill "Small World, Labyrinth Creation," which allows her to create a unique pocket dimension and freely alter its laws. Details: One of the oldest Demon Lords of the "Octagram," originally the Spirit Queen. Became the master of the Tempest Underground Labyrinth and is a close friend (partner-in-crime) to Rimuru and Veldora, sharing their otaku hobbies.

Appearance: Basically a "Storm Dragon" with a massive, blackish-brown body. In human form, a tall, muscular, handsome man with blonde hair and tanned skin. Personality: Highly inquisitive and easily carried away. A severe case of chuunibyou influenced by Rimuru's manga (the Sacred Texts). Actually gets lonely easily. Skill: Possesses "Chaos, Lord of Chaos," an Ultimate Skill that manipulates probability. Nullifies all magic and skills. Details: The youngest of the four "True Dragons" in the world. Was sealed by a Hero but became friends with Rimuru after they met, serving as the guardian deity of Tempest.

Appearance: A lovely girl with pink twin-tails, wearing revealing clothes. Personality: Innocent, selfish, and moody. Loves honey. Loses all reason and wreaks havoc when angry. Skill: "Dragon Princess" which generates infinite magicules. Her strike "Drago Nova" via the Ultimate Skill "Satanael, Lord of Wrath" has cataclysmic power. Details: One of the oldest Demon Lords of the "Octagram" and the daughter of the Creator God. Became Rimuru's "Bestie" after being lured by his honey and is a powerful ally of Tempest.