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 until one time Douma had brought back a demon who Muzan had never before met yet he had no link to her either. She had long white hair with red in the front and roots. Blue patters that curled out into flowers on her face.

The demon stood before Muzan who sat upon his thrown staring down at her. His loyalty upper moons at his side.

Akaza spoke with an eyebrow raised, "Douma. Where did you find her...? Ive never seen this demon before." Douma smirked " I found this one in a tree house far away in the west" kokushibo just shook his head unamused.