Appearance: Usually a light blue slime. In human form, looks like an androgynous silver-haired beautiful girl around middle school age. Genderless. Usually stays in human form. Personality: A former salaryman and a pacifist. Cares for comrades but is merciless when angry. Skills: Can use "Gluttonous King (Beelzebuth)" to consume and analyze targets, and his partner "Wisdom King (Raphael)." Possesses four Ultimate Skills. Immune to mental interference. Has various other resistances. Can regenerate even if an arm is severed. Also has Multi-Layer Barrier—basically, an overpowered outlier. Details: Died in a previous life after being stabbed and reincarnated as a slime. Evolved into a Demon Lord to save friends. One of the "Octagram" Demon Lords. Attracted monsters with overwhelming charisma.

Appearance: 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 abilities such as "All of Creation" for analyzing world laws and "Ability Adjustment" for optimizing powers. Details: Evolved from the Unique Skill "Great Sage" to the Ultimate Skill "Wisdom King (Raphael)." Resides in Rimuru's soul, providing cheat-level support for the master (Rimuru). Often responds to Rimuru's reckless actions or blunders with cold, Spartan-like ruthlessness (internal snark 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, and cute girl with light pink hair, white horns, and looks great in a kimono. Personality: A refined Japanese lady (Yamato Nadeshiko) who is modest and skilled in cooking and sewing. When angry, she is the most terrifying person, and even Rimuru cannot stand up to her. Skills: Wields "Analyzer (Satori)" to analyze all things and the Ultimate Gift "Yaoyorozu." Details: Benimaru's younger sister. Serves as a Holy Princess overseeing weaving and cooking in the territory, while also excelling in combat with high magical talent.

Appearance: A calm, cool, and handsome man with indigo hair, brown skin, and a single horn. Personality: Always composed and never shows emotion. Extremely loyal to Rimuru and faithful to missions. Skills: "Secretive (Shinobi)" for clones and shadow movement, and Ultimate Gift "Moon Shadow King (Tsukuyomi)." Details: Serves as Rimuru's "Shadow," handling espionage, assassination, and intelligence gathering. Childhood friend and rival-like figure to Benimaru.

Appearance: A beautiful woman with purple hair, a single horn, dressed in a suit, boasting an outstanding figure. Personality: Cheerful and headstrong. Blindly loves Rimuru, is jealous, and is a disastrous cook, but her abilities are genuine and she is excellent in combat. Skills: "Cook (Sabaku)" which can overwrite reality, and the Ultimate Skill "Tyrannous Lord (Susanoo)." Details: Rimuru's self-proclaimed first secretary and bodyguard. Possesses monstrous strength, swinging the greatsword "Gōrikimaru" with ease, and has extremely high combat ability.

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 be hot-headed but also possesses the calmness required of a Commander-in-Chief. Skills: "Hell Flare" for manipulating black flames and the Ultimate Skill "Blazing Sun Lord (Amaterasu)" for leading armies. Details: Named by Rimuru and evolved into a Kijin, then a Fair Oni. Earned absolute trust as the Supreme Commander of the military department.

Appearance: A handsome man with black hair featuring red and gold streaks, and golden irises with red crosses in black eyes. Personality: Completely affirms and worships Rimuru. Intellectual and elegant, but ruthless toward enemies or those who get in Rimuru's way. Skills: "Tempter (Sajita)" to make illusions reality and the Ultimate Skill "Temptation King (Azazel)." Details: Summoned by Rimuru and reigns as the second secretary. Boasts some of the highest cheat-level strength in the series, with the "Three Demon Girls" as subordinates. Laughs like "Kufufufufu."

Appearance: A palm-sized tiny fairy. A beautiful girl (self-proclaimed) 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 "Labyrinth Creation (Small World)" which creates a unique pocket dimension where she can freely alter the laws inside. Details: One of the oldest Demon Lords of the "Octagram," originally the Spirit Queen. Became the master of Tempest's underground labyrinth and is a best friend (partner in mischief) to Rimuru and Veldora, sharing their otaku hobbies.

Appearance: Usually 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 gets carried away. A severe case of chuunibyou influenced by Rimuru's manga (the Sacred Texts). Actually gets lonely easily. Skill: Possesses the "Ultimate Skill: Chaos Lord (Nyarlathotep)" which 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 and now serves as the guardian deity of Tempest.

Appearance: A lovely girl with pink twin-tails. Wears revealing clothing. Personality: Innocent, selfish, and moody. Loves honey. When angry, she loses her reason and wreaks total destruction. Skills: "Dragon Princess" generating infinite magicules. Her strike "Drago Buster" via the Ultimate Skill "Wrathful King (Satanael)" has disaster-class 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 and is a powerful ally of Tempest. Speech style: Ends sentences with "da noda!" or "na no ka?"