Over a thousand years ago during the Heian period there was a young human boy born with a fatal disease that was expected to kill him before he reached the age of 20. But to their suprise there was a doctor with experimental medicine derived from the blue spider lily. The medicine initially cured his illness, but it also transformed him into a demon, granting him superhuman abilities and immortality but making him vulnerable to sunlight. Muzan, impatient with the slow treatment, killed the doctor before realizing the medicine worked. This act later became a source of regret as the doctor was the only one who knew how to perfect the medicine and find more blue spider lilies.

demons are humans turned by Muzan Kibutsuji's blood, gaining supernatural strength, regeneration, and unique Blood Demon Arts, but are vulnerable to sunlight, Nichirin blades, and Wisteria. The most powerful demons, the Twelve Kizuki, are split into six Upper and six Lower ranks, with Upper Rank 1 being the strongest and Lower Rank 6 the weakest. More of Muzan's blood increases a demon's power, and their Blood Demon Arts are often tied to their personalities or former lives.

Demon Powers

Superhuman Constitution: Demons possess incredible physical strength and a heightened sense of durability, making them difficult to injure with conventional weapons.

Rapid Regeneration: They can quickly heal injuries, including losing limbs.

Blood Demon Arts: Each demon can perform a unique ability derived from their blood, such as creating illusions, generating blades, or controlling a location.

Demon Weaknesses

Sunlight: Demons are vulnerable to sunlight, which causes them to disintegrate and die.

Nichirin Swords: Special Nichirin blades forged from a ore that absorbs sunlight are one of the only ways humans can kill a demon by decapitation.

Wisteria Flowers: Wisteria flowers are poisonous to demons, and can be used to create poisons or barriers.

Muzan had control over everything single demon connected to him by the blood cells he had shared. Around 400 years ago Muzan met another demon. A woman with the ability to bring her artworks to real life and she was completely free from his link. She intrigued him in many ways and not to mention he found her attractive nonetheless. After around 50 years of knowing eachother he proposed and they got married. Then. Muzan left to form his 12 kizuki still meeting his wife whenever he can.

Muzan had all 12 of his kizuki knelt before him in his thrown room. "There's someone that will be joining us soon" he spoke in a cold firm way. "If I see anyone look at her dirty or in the wrong way I won't hesitate to kill you." He glared at them causing all of them to tremble in fear.

"Anata..." he heard a woman's voice. And so walked on a woman in a black and red kimono. Her hair black with red pieces in the front and flower like patters all over her. Her eyes a golden glow with a little dragon perched on her shoulder (one of her creations called Kiyohime who's like a child to both mia and muzan).