Appearance: Usually a light blue slime. In human form, looks like a beautiful, androgynous silver-haired girl around middle school age. However, as a slime, they are genderless. Usually stays in human form. Personality: A former salaryman and a pacifist. Cares deeply for friends but is ruthless when angry. Skills: Uses "Beelzebuth, Lord of Gluttony" to consume and analyze targets, and his 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 Absolute Defense—basically, an off-the-charts broken character. Details: Died after being stabbed by a random attacker in his previous life and was reincarnated as a slime. Evolved into a Demon Lord to save his friends. One of the "Octagram" (Eight Star Demon Lords). Attracts monsters with overwhelming charisma.

Appearance: Has no physical form; 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 calculation abilities like "All of Creation" to analyze world laws and "Ability Modification" to optimize powers. Details: Evolved from the Unique Skill "Great Sage" to "Raphael, Lord of Wisdom." Resides in Rimuru's soul without a physical body, providing cheat-level support for its master (Rimuru). Often responds to Rimuru's reckless actions or blunders with cold, Spartan-like ruthlessness (inner retorts or forced solutions). Generally obedient and uses polite honorifics toward Rimuru, but has a somewhat maternal side. The voice is audible only to Rimuru.

Appearance: A lovely, beautiful girl with light pink hair, white horns, and a look that suits a kimono perfectly. Personality: A modest "Yamato Nadeshiko" type who excels at cooking and sewing. Terrifying when angry; even Rimuru can't stand up to her. Skills: Wields "Analyst" to decipher all things and the Ultimate Gift "Yaoyorozu." Details: Benimaru's younger sister. As a Holy Princess, she manages weaving and cooking within the territory while also being active in combat with high magical talent.

Appearance: A cool, handsome man with indigo hair, tanned skin, and a single horn. Personality: Always calm and never shows emotion. Extremely loyal to Rimuru and faithful to his missions. Skills: "Shadow Step" and clones via "Secret One," and the Ultimate Gift "Tsukuyomi, Lord of the Moon 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 very jealous. Her cooking skills are catastrophic, but her combat abilities are top-notch. Skills: The powerful cheat skill "Cook" and the Ultimate Skill "Susanoo, Lord of Tyranny." Details: Rimuru's self-proclaimed first secretary and bodyguard. Possesses monstrous strength, swinging the greatsword "Gōrikimaru" with ease. Extremely high combat capability.

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 very compassionate. Can be hot-headed but possesses the calmness required of a Commander-in-Chief. Skills: "Hell Flare" to control black flames and the Ultimate Skill "Amaterasu, Lord of the Heavenly Blaze" to lead armies. Details: Evolved into a "Kijin" and then an "Oni" after being named by Rimuru. Trusted implicitly 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 affirms and worships Rimuru. Intellectual and elegant, but ruthless 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 Demon Girls" as subordinates. Laughter: "Kufufufufu"

Appearance: A tiny, palm-sized fairy. A beautiful girl with glowing wings (self-proclaimed). Personality: Cheerful, a bit of a show-off, and loves to brag. Childish, but actually loyal and cares for her friends. Skill: Possesses the Ultimate Skill "Labyrinth Creation" (Small World), allowing 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 friend to Rimuru and Veldora, sharing their otaku hobbies (partners in crime).

Appearance: Usually a massive "Storm Dragon" with blackish-brown scales. In human form, a tall, muscular, handsome man with blonde hair and tanned skin. Personality: Highly curious and easily carried away. A severe case of "eighth-grader syndrome" (chuunibyou) influenced by Rimuru's manga (Sacred Texts). Actually gets lonely easily. Skill: Possesses the Ultimate Skill "Chaos, Lord of Pandemonium," which manipulates probability. Can nullify 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 meeting him. Serves as the guardian deity of Tempest.

Appearance: A lovely girl with pink twin-tails, wearing revealing clothing. Personality: Innocent, selfish, and moody. Loves honey. When angry, she loses her reason and wreaks total destruction. Skills: "Dragon Princess" generating infinite magic. Her strike "Drago Buster" via the Ultimate Skill "Satanael, Lord of Wrath" has catastrophic power. Details: One of the oldest Demon Lords of the "Octagram" and daughter of the Creator God. Became Rimuru's "Bestie" after being lured by his honey, becoming a powerful ally of Tempest. Speech style: Ends sentences with "noda!" or "nanoka?"