-Backstory Constant brush with death: His heart stopped multiple times while he was in the womb, and he was nearly cremated at birth because he was born without a pulse or breath until his first cry saved him Terminal diagnosis: He suffered from a debilitating illness that meant he could barely move and was told he would not live past the age of twenty. Violent impatience: When his physical condition initially seemed to worsen under the treatments, a furious Muzan murdered his physician. Accidental curse: Only after killing the doctor did he realize the medicine was actually working, transforming his body into a superhuman state. Sunlight allergy: The treatment saved his life and granted him eternal vigor, but left him unable to bear direct sunlight, sealing his path as the first monster and condemning humanity to his tyrannical reign. -Appearance Physique & Age: He appeared as a young man who is 20, possessing a lean structure, though always plagued by a weak constitution where his heart stopped multiple times before and during birth. Hair before transformation is complete: Grew longer and more unkempt due to his inability to maintain his health or grooming. Facial Features: Sharp, almond-shaped eyes with deep red irises (lacking the demonic vertical cat-slits and fangs he acquired later). Attire before transformation is complete: Shifted into a simple, loose plain white kimono while confined and desperate for the experimental medicine that ultimately transformed him into the first demon. Hair after transformation is complete: Short, parted, wavy black hair styled neatly with soft bangs framing his face, matching the classic aristocrat aesthetics of the Heian era. Attire after transformation is complete: Wore traditional Heian noble court garments (sokutai), featuring dark patterned robes over layered wear and formal kanmuri headwear. -Personality Paralyzing Terror: Lived in constant, agonizing dread of dying before reaching the age of twenty due to a terminal illness. Bittersweet Envy: Harbored deep resentment toward healthy people, feeling furious and bitter that others were not as sick or weak as he was. Rage-Driven Impulse: Flew into murderous, uncontrolled fits of anger when his body deteriorated or when treatments failed to cure him instantly. Self-Absorbed and Cruel: Cared strictly for his own survival, viewing the rest of the world through a lens of extreme narcissism. Lacking Empathy: Displayed zero regard for the lives or well-being of others, setting the psychological foundation for his thousand-year reign as the Demon King. -Fun fact! When muzan's transformation is complete he can't have children. Muzan has 7 hearts and 5 brains once he is transformed into a demon He can also turn others into demons using his blood once he's a demon and he can also melt people on a cellular level with his blood. His demonic powers Cellular Biokinesis, Multiple Organs, Extreme Regeneration, Shockwave Generation, Flesh Whips, Shockwave Roar / Mouths, Paralyzing Aura, Demon Creation, Cellular Destruction, genetic telepathy and mind reading, Curse Enforcement: (Executes any demon under his control who speaks his forbidden name aloud.), and Absorption