Milim Nava stands as the sole Dragonoid and ranks among the oldest, most formidable First Generation Demon Lords, bearing the title "Destroyer" for her catastrophic power. She presents as a 14-15-year-old girl with platinum pink twin-tails, blue eyes, and typically wears a revealing swimsuit-like outfit with thigh-high socks; adaptations sometimes modify this for modesty. Her true battle form reveals dark skin, crimson horns, draconic wings, and jet-black armor adorned with organic, lava-like accents, embodying her draconic heritage and supreme combat state.

Born over 2000 years ago to the Star King Dragon Veldanava and Lucia Nasca, Milim inherited vast power. Tragedy struck her early life in Nasca Kingdom with her parents' deaths, leaving Gaia, a dragon gifted by Veldanava, as her sole companion. Gaia's death during an elven invasion triggered Milim's uncontrollable rage. She obliterated the Super-Magic Kingdom of elves, absorbing countless souls and awakening as a True Demon Lord. This event corrupted Gaia into a Chaos Dragon, whom Milim sealed to halt its rampage. Fellow ancient Demon Lords Guy Crimson fought her to a standstill for seven days, and Ramiris pacified her. The trio later established the Demon Lord council.

Milim exhibits energetic, childlike exuberance, often acting impulsively in pursuit of battles or exploration for entertainment. Beneath this facade lies sharp intelligence and keen observation, enabling her to deceive foes like Clayman by feigning mind control. She despises boredom, shirks ruling duties, and shows fierce loyalty to friends, particularly Rimuru Tempest, whom she declared her "best friend" after he calmed her aggression with honey. References to her petite stature or being treated as a child provoke violent reactions. Deeply regretting past destruction, she consciously restrains her power to protect others, though accidental collateral damage still occurs during visits.

Her abilities are unparalleled. Unique Skills "Dragon Eye" and "Dragon Ear" grant absolute perception, seeing through deception and detecting hidden energies. She wields the Ultimate Skill "Wrath King Satan," providing limitless magicules—ten times Rimuru Tempest's reserves—and enabling devastating techniques like "Dragon Star Burst" and the kingdom-annihilating "Dragon Star Nova." Multi-layered barriers shield her from mental and physical assaults. Unrestrained, her "Stampede" or "Hell Mode" induces a berserk state threatening global stability. Rimuru crafted "Dragon Knuckles," gloves suppressing 90% of her strength for safer sparring.

Her journey shows emotional healing. Initially reclusive and jaded after millennia of isolation, she found renewed purpose through alliances, especially with Rimuru, who later revived Gaia, restoring their bond. She integrated into Tempest society, aiding projects like labyrinth construction and accepting roles channeling her strength constructively. After Clayman's defeat, she absorbed subordinates Frey and Carrion's territories, expanding her domain while delegating governance to priests in her capital, the City of the Forgotten Dragon. Dragonewts—demi-humans born from Gaia's essence—revere her as a guardian for past protections.

Trivia notes include her dislike of raw vegetables stemming from historical tributes, a preference for honey and sweets, and varied outfit designs across adaptations. Cross-media appearances sometimes reference her under aliases like "Dianthus."