Rimuru Tempest began existence as Satoru Mikami, a 37-year-old Japanese salaryman reborn as a slime following a fatal stabbing while shielding a coworker. Initially manifesting as a spherical, translucent blue slime 40 cm wide, this form doubles in size upon evolving into an Ultimate Slime. The slime’s surface shifts into metallic or golden hues when activating Body Armor or Demon Slime transformations. A humanoid form is adopted by replicating the appearance of Shizue Izawa, a deceased adventurer whose remains were absorbed, presenting as an androgynous adolescent with silver-blue hair and golden eyes. This form matures from a childlike stature to that of a teenager, with attire reflecting power stages such as demon lord seed or ultimate slime phases. Deliberately genderless in design, Rimuru’s ambiguous presentation leans into an androgynous aesthetic across adaptations. Mental identity retains a male-leaning perspective from Satoru’s memories, though external perceptions fluctuate between gendered interpretations. The humanoid form remains anatomically neutral, avoiding explicit features. Personality merges Satoru’s human ethics with a monster’s pragmatic, calculating mindset. Prioritizing a harmonious world, Rimuru balances idealism with strategic ruthlessness. Diplomatically adept, they forge alliances and extend forgiveness to former foes yet unleash merciless retaliation—torture, memory erasure, or annihilation—when allies are threatened. Openly self-identifying as socially inept ("KY"), Rimuru diffuses tension with humor but grapples with anxiety, self-doubt, and impostor syndrome, relying on allies like King Gazel for guidance. Immortality fuels existential contemplation of loneliness and attachment to mortal companions. Abilities stem from unique reincarnation-granted skills, amplified by consuming entities and evolution. Initial powers include Predator (absorption/mimicry), Great Sage (analytical intelligence), and Magic Sense. Key milestones transform Predator into Gluttony, then Beelzebuth post-demon lord ascension, while Great Sage evolves into Raphael and later Ciel, gaining autonomous problem-solving. Additional skills like Poison Gas, Thread Manipulation, and Magical Barrier complement combat tactics favoring spell combinations—Black Flame or sunlight-focused Megiddo. True Demon Lord evolution during the Harvest Festival bestows immortality, amplifies magic, and empowers subordinates. Leadership centers on founding the Jura Tempest Federation, a monster nation advocating interspecies equality. Diplomatic alliances with human kingdoms and demon lords pair with infrastructure projects informed by Satoru’s corporate background. Naming monsters induces evolution and loyalty, cultivating powerful subordinates like Benimaru and Shion. Governance blends benevolence with calculated deception, including historical revisionism to craft a benevolent image. Relationships, such as with the freed True Dragon Veldora Tempest, emphasize mutual respect and familial bonds forged through shared naming. Development spans adaptation to monster physiology, reconciling human morals with pragmatic rule, and embracing demon lord duties. Early aversion to killing humans shifts after tragedies like the Falmuth invasion, though anime adaptations temper this moral struggle. Later arcs explore balancing godlike power with humility, sustaining optimism amid political intricacies, and confronting existential fears tied to eternal life.