Rimuru Tempest began existence as Satoru Mikami, a 37-year-old Japanese salaryman who perished protecting a colleague from a stabbing. An unidentified voice, responding to his final thoughts, reincarnated him as a slime in a fantasy world. His new form manifested as a small, translucent blue sphere roughly 40 cm in diameter, expanding to 70-100 cm as his power grew. Early in this existence, he encountered the sealed Storm Dragon Veldora, forging a profound bond. They exchanged names—Satoru becoming Rimuru Tempest, sharing Veldora's surname—and Rimuru absorbed the dragon to analyze and eventually break the sealing magic, storing Veldora within his body. As a slime, Rimuru inherently lacks gender or sex organs, a universal trait for his species. After devouring the deceased adventurer Shizue Izawa, he gained a human-like form. This form appears androgynous, initially resembling a child aged 6-7 with silver-blue hair and golden eyes, later maturing to look 15-16 years old following further power increases. The author explicitly confirmed Rimuru as genderless, possessing no biological sex. Early translations often used male pronouns due to his past life memories, but Rimuru self-identifies as gender-neutral. His human form lacks reproductive organs or human biological needs like breathing or excretion, though he can consume food and drink for pleasure. His attire varies, including practical gear like fur coats or armor, but subordinates frequently dress him in ornate, feminine clothing without his objection. His personality blends Satoru's human experiences with slime traits. He exhibits a generally laid-back, quirky demeanor, often sidestepping trouble but working diligently when required. His salaryman background fosters a polite, accommodating nature, making it difficult to refuse requests and leading to overwork. Rimuru is intensely protective of subordinates, friends, and citizens of his nation, reacting severely to threats against them—a stark contrast to his usual cheerfulness. This protectiveness coexists with strategic ruthlessness; he employs torture, intimidation, or annihilation against enemies without hesitation if they harm his allies. Early diplomatic naivety and anxiety gradually yield to calculated leadership as he adapts to his role. He values peace and cooperation but acknowledges that ideals require power to uphold, driving him to pursue strength pragmatically. Core abilities originate from skills granted during reincarnation and assimilation. Predator, evolved into Gluttonous King Beelzebuth and later Void God Azathoth, allows consumption of targets to acquire their skills, forms, or memories, including souls and magic. Great Sage, which evolved into Raphael and then Ciel, provides analysis, skill replication, and autonomous problem-solving, enabling rapid learning, such as instantly copying spells from books. Mimicry permits assuming absorbed forms, while Shapeshifting allows partial transformations like wings or armor. Evolving into a True Demon Lord increased his magic reserves tenfold and granted Immortality. Later advancements unlocked spacetime manipulation through Instantaneous Movement and Time Warp, dimensional barriers via Multi-Dimensional Barrier, and destructive energies like Turn Null. Combat proficiency includes swordsmanship training from the sword saint Hakurou and tactical innovation, exemplified by creating the sunlight-based Megiddo spell. Following Veldora's disappearance, which created a power vacuum, Rimuru founded the Jura Tempest Federation in the Great Forest of Jura. He united monsters—goblins, direwolves, ogres, orcs—by naming them, unlocking their latent potential and evolving them, while fostering a multicultural society. His leadership emphasizes meritocracy, diplomacy, and technological innovation inspired by his human memories, such as manga reproduction and modern infrastructure. Naming creates a soul-link lineage, granting shared power boosts; his ascension to True Demon Lord enhanced all named subordinates. He actively pursues alliances with human and monster nations, though his ideal of coexistence faces challenges from human supremacist factions and hostile Demon Lords. His evolution progressed from slime to Demon Lord Seed after absorbing the Orc Lord, then to True Demon Lord following the massacre of Farmus soldiers. This massacre triggered a ritual sacrificing 10,000 souls to revive his slain citizens. Later, he became an Ultimate Slime after integrating True Dragon traits. This growth reflects increasing detachment from human morality; early reluctance to kill gives way to pragmatic annihilation of threats. For instance, he decimated the Farmus army with Megiddo and later manipulated political narratives to portray Tempest as a victim, justifying retribution. Despite this, his core goal remains creating a world where all beings coexist peacefully.