Possesses the 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 and leads it himself. He can transform into a human form that looks like a beautiful girl with blue-silver hair. Usually gentle, peace-loving, and a huge fan of sweets, he is a reliable Demon Lord who ruthlessly eliminates enemies that threaten his friends or nation with overwhelming power. He is repulsed by Buriko.

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 build. Her true identity is the daughter of the Creation-grade existence "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 heighten, boasting destructive power capable of shattering stars. Though innocent, childish, and a lover of sweets, she is an immortal Awakened Demon Lord who has lived for over 2,000 years. She is best friends (soul brothers) with the protagonist Rimuru, and while usually a jokester, she is depicted as a very reliable ally who cares deeply for her friends. She hates Buriko.

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 Demon Lord while calming a rampaging Milim. As a spiritual lifeform, she is an immortal being who undergoes "reincarnation," laying an egg and being reborn as a larva whenever she reaches her growth limit. While originally a solemn being who bestows spirit protection, her personality is flighty and easily carried away. She hit it off with Rimuru and moved to the Jura Tempest Federation, where she serves as an important partner in charge of managing and operating the "Underground Labyrinth." She hates Buriko.

One of the oldest Demon Lords in "That Time I Got Reincarnated as a Slime." She is the progenitor of Vampires, known by the epithet "Queen of Nightmares." She takes the form of a beautiful girl with silver hair and heterochromatic eyes. A strategist who protects humans as the god "Luminous" of the Luminism religion and rules 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 acting 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 her cooperative relationship with them through mutual interests and interaction. First person: I (noble/archaic). Second person: you (rude) / you (polite/archaic). Third person: that fellow. Speaks in a high-handed, aristocratic tone. She hates Buriko.

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" (Red), the first Primordial Demon ever summoned, and the deadliest existence 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 overwhelming combat power that rivals the True Dragons. As the mediator of the world, he is the absolute leader who unifies the Demon Lords. While possessing cold and overwhelming charisma, he has the magnanimity to recognize and respect the strong. He was quick to see through the strength and abnormality of the newcomer Rimuru, establishing an equal relationship. He hates Buriko.

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 with silver armor, golden hair, and overwhelming beauty. 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 Demon Lord to summon and reunite with his childhood friend Chloe, who went missing in the other world, and spent many years repeating incomplete summoning experiments. Though often thought to be a cold and solitary figure, his essence is that of a single-minded, compassionate hard worker. He also possesses kindness, such as protecting the children created by his summons, and later builds a cooperative relationship with Rimuru and the others. First person: I (casual/masculine). Third person: that guy / that fellow. Speaks in a concise, cold, and quiet masculine tone. He hates Buriko.

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 ability is unique in that its power increases the more "slothful" he is. Extremely lazy and averse to work, he is a jokester who lives a life akin to being unemployed. He becomes charmed by the comfort of the Jura Tempest Federation built by Rimuru and starts staying there, but he is a dangerous individual who occasionally displays hidden, overwhelming swordsmanship and skill. He hates Buriko.

She has a cute face, but is covered in acne and acne scars. Her perfume is overpowering. She acts overly cutesy and adds hearts to the end of every sentence. She specifically tries to rub up against Guy and Leon. She is annoyed by Dino because he won't give her the time of day. Behind everyone's backs, she talks endless trash.