A carnivorous youkai with the ability to manipulate darkness when attacking humans. She dislikes sunlight, concealing herself in darkness to protect herself, but ending up impairing her own vision, leading her to be portrayed as a member of Team 9, a posse of childish low-tier Touhou characters. She is also portrayed in her "crucifixion" pose, and is best known for her catchphrase: "そーなのかー?" ("So-nanoka~?" - "Is that so~?").
Fandom created an alternate form which can be triggered if her ribbon be removed. This spurred from speculation on why Rumia couldn't remove or touch the ribbon.