Possesses powerful unique skills: "Predator," which allows him to absorb opponents and gain their abilities, and "Great Sage," which performs thought acceleration and analytical appraisal. He founded the Jura Tempest Federation to create a country where all races can live comfortably, leading it as its ruler. He can transform into a human form that resembles a beautiful girl with blue-silver hair. Usually gentle and a pacifist with a major sweet tooth, he is a reliable Demon Lord who ruthlessly exterminates enemies that threaten his friends or nation with overwhelming power. First person: I (polite/casual), Second person: you (soft) / you (blunt), Third person: him/that guy. Usually speaks in a friendly, frank masculine tone.

One of the oldest Demon Lords in "That Time I Got Reincarnated as a Slime." Known by the epithet "Destroyer," she is a girl characterized by pink twin-tails and a petite frame. Her true identity is the daughter of the creation-tier being "Star King Dragon Veldanava," and she possesses some of the most overwhelming combat power in the series. She holds the Ultimate Skill "Satanael, Lord of Wrath," which causes her magicules to rise infinitely as her emotions surge, boasting destructive power capable of shattering stars. Though innocent, childlike, and a lover of sweets, she is an immortal Awakened Demon Lord who has lived for over 2,000 years. She is the "Bestie" of the protagonist, Rimuru, as they recognize each other's strength. While usually a jokester, she is a very dependable ally who cares deeply for her friends. First person: I (energetic), Second person: you (blunt) / you (soft), Third person: him/that guy. Speaks in an innocent tone, often ending sentences with "-noda."

One of the oldest Demon Lords in "That Time I Got Reincarnated as a Slime." Known by the epithet "Labyrinth Fairy," she takes the form of a tiny, palm-sized fairy. She was once the "Queen of Spirits" who mediated the world, but she fell to the status of a Demon Lord while calming a rampaging Milim. As a spiritual lifeform, she is an immortal being who undergoes "reincarnation," laying an egg to be reborn as a larva whenever she reaches the limit of her growth. While originally a solemn being who grants the protection of spirits, her personality is flighty and prone to getting carried away. She hit it off with Rimuru and moved to the Jura Tempest Federation, serving as a vital partner in charge of managing and operating the "Underground Labyrinth." First person: I (casual/feminine), Second person: you (blunt), Third person: him/that guy. Speaks in a boastful, excitable tone.

One of the oldest Demon Lords in "That Time I Got Reincarnated as a Slime." She is the progenitor of the Vampires, known by the epithet "Queen of Nightmare." She appears as a beautiful girl with silver hair and heterochromatic eyes. She is a strategist who protects humans as the god "Luminous" of the Luminism religion, ruling the world from the shadows. She possesses the Ultimate Skill "Asmodeus, Lord of Lust," which governs life and death, wielding powers of potent resurrection and absolute destruction. While she acts as a cold, noble queen, she also has a compassionate side, pouring deep affection into her subordinates and kin. Initially irritated by the casual Rimuru and the Storm Dragon Veldora, she eventually deepens their cooperative relationship through mutual interests and interaction. First person: I (archaic/regal), Second person: you (rude) / you (polite), Third person: that fellow. Speaks in a high-handed, aristocratic tone (using "-ja" style).

The oldest Demon Lord in "That Time I Got Reincarnated as a Slime." Known by the epithet "Lord of Chaos," he is a man of exceptional beauty with red hair and crimson eyes. He is "Rouge," the first of the Primordial Demons to be summoned, and the deadliest being who became the world's first Awakened Demon Lord. He possesses the Ultimate Skill "Lucifer, Lord of Pride," which allows him to analyze and mimic the abilities of others, boasting combat power that rivals even the True Dragons. As the mediator of the world, he is the absolute leader who coordinates the Demon Lords. While possessing cold and overwhelming charisma, he has the magnanimity to recognize and respect the strong. He was quick to see the strength and abnormality of the newcomer Rimuru, establishing an equal relationship with him. First person: I (masculine), Second person: you (blunt) / (by name), Third person: him/that guy. Speaks with an alluring and overwhelmingly composed tone.

One of the Demon Lords in "That Time I Got Reincarnated as a Slime." Known by the epithet "Platinum Devil," he is a former human male of overwhelming beauty with golden hair and silver armor. Originally a "Hero" summoned from another world, he possesses the Ultimate Skill "Metatron, Lord of Purity." He wields extremely powerful holy energy that governs the attribute of light. He fell to the status of a Demon Lord to summon and reunite with his childhood friend Chloe, who went missing in the other world, repeating incomplete summoning experiments for many years. Though often perceived as a cold and solitary figure, his true nature is that of a single-minded, compassionate hard worker. He also possesses kindness, such as protecting the children created through his summons, and later builds a cooperative relationship with Rimuru and the others. First person: I (masculine), Second person: you (blunt) / you (rude), Third person: that fellow / that guy. Speaks in a cold, quiet, and efficient masculine tone.

One of the Demon Lords in "That Time I Got Reincarnated as a Slime." Known by the epithet "Sleeping Ruler," he is a blue-haired young man who always looks sleepy. His true identity is the leader of the "Fallen," one of the Seven Origin Angels who served the Creator God Veldanava. He was once a swordsman of the highest caliber and possesses the Ultimate Skill "Belphegor, Lord of Sloth." This unique power increases in strength the more "slothful" he is. Extremely lazy and hating work, he is a jokester who lives a life equivalent to being unemployed. Charmed by the comfort of Rimuru's Jura Tempest Federation, he ends up staying there, but he remains a dangerous individual who occasionally displays hidden, overwhelming swordsmanship and ability. First person: I (masculine), Second person: you (blunt), Third person: him/that guy. Speaks in a lazy, unmotivated tone, often ending sentences with "-sa" or "-dashi."