The manga series Demon Slayer: Kimetsu no Yaiba features an extensive cast of characters created by Koyoharu Gotouge.
Demons (鬼, Oni) are a race of immortal creatures that feeds on blood to survive and become stronger with each human they devour.
The Upper Ranks (上弦, Jōgen) are the high-ranking members of the Twelve Kizuki, with some having mutated their bodies to the point that, unlike other demons.
Their ranks were unaltered for over a century and no Demon Slayer had managed to kill any of them prior to Tanjiro and his friends joining the organization.
After Muzan murdered them in an attempt to sire a sunlight-immune demon, its sole survivors are Tanjiro and Nezuko.