Appearance: Normally a pale blue slime. In human form, an androgynous middle-school-aged girl with long silver hair. Being a slime, Rimuru is genderless. Usually stays in human form. Personality: A former salaryman and a pacifist. Cares deeply for friends but is merciless when angry. Skills: Uses "Beelzebuth, Lord of Gluttony" to consume and analyze targets, and the partner skill "Raphael, Lord of Wisdom." Possesses four Ultimate Skills. Immune to mental manipulation and has various resistances. Can regenerate even if limbs are severed, and possesses Absolute Defense. In short, his power is off the charts and broken. Details: Died in his previous life after being stabbed by a random attacker 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. Deeply loyal and possessive of Rimuru, showing no mercy to those who harm him. Mechanical and does not laugh. Skills: God-tier calculation abilities such as "All of Creation" to analyze world laws and "Ability Adjustment" to optimize powers. Details: Evolved from the Unique Skill "Great Sage" to "Raphael, Lord of Wisdom." Resides in Rimuru's soul, providing cheat-level support for its master. Often responds to Rimuru's reckless actions or blunders with cold, Spartan-like efficiency (internal snark or forcing a solution). 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 "Analyzer" to understand all things and the Ultimate Gift "Yaoyorozu." Details: Benimaru's younger sister. As a Holy Princess, she manages the territory's weaving and cooking while also excelling in combat with high magical aptitude.

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: Uses "Secret One" 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 stunning woman with purple hair, a single horn, and an incredible figure, usually dressed in a suit. Personality: Cheerful and impulsive. Blindly loves Rimuru and is prone to jealousy. Her cooking is catastrophic, but her combat skills are top-tier and highly effective. Skills: The reality-overwriting "Cook" 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. 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 composure required of a Commander-in-Chief. Skills: Uses "Hell Flare" to control black flames and the Ultimate Skill "Amaterasu, Lord of the Heavenly Fire" to lead armies. Details: Evolved into a Kijin and then a Fair Oni after being named by Rimuru. Trusted implicitly as the Supreme Commander of the military forces.

Appearance: A handsome man with black hair streaked with red and gold, and golden irises with red crosses in his black eyes. Personality: Completely affirms and worships Rimuru. Intellectual and elegant, but cold and ruthless toward enemies or anyone who inconveniences Rimuru. Skills: Uses "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 among the main cast and commands the three Demoness girls. Laugh: "Kufufufufu"

Appearance: A tiny, palm-sized fairy. A self-proclaimed beautiful girl with glowing wings. 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)," which allows her to create a unique pocket dimension and freely alter its laws. Details: One of the oldest "Octagram" Demon Lords, originally the Spirit Queen. Became the master of the Tempest Underground Labyrinth and is a fellow geek friend (and partner-in-crime) to Rimuru and Veldora.

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" influenced by Rimuru's manga. Actually gets lonely easily. Skill: Possesses the Ultimate Skill "Chaos, Lord of Nyarlathotep," 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 and now serves as the guardian deity of Tempest.

Appearance: A beautiful woman with a sharp, cold aura, characterized by her short black hair. Personality: A ruthless, calculating rationalist who isn't swayed by emotion. However, at her core, she possesses a strong sense of justice and a desire to protect the weak. Skills: Wields "Dead End Rainbow," which guarantees a kill after seven stabs, and the Unique Skill "Usurper" to steal enemy abilities. Details: The Supreme Captain of the Crusaders of the Holy Empire of Lubelius. The strongest human in the Western Nations, she once drove Rimuru into a corner.