A female devil. Stage 4 midboss of Touhou's Embodiment of Scarlet Devil who lives in the Scarlet Devil Mansion, often seen in the Voile Library. She has long red hair, demon wings and bat-like head wings. She has a demon tail and full demon wings on her back in some pictures.
It is generally assumed by the majority of fans that Koakuma is Patchouli's summoned familiar and personal assistant, as she is rarely seen outside of the library unless accompanying the magician, and served as Patchouli's midboss in EoSD. She's also frequently depicted as a succubus in fanworks, despite ZUN calling her more of an imp and her exact species being unknown.
Unused sprites in the EoSD game files include a possible "EX-Koakuma" with violet hair and a purple arcane aura, which might have been meant to appear alongside Patchouli during the Extra Stage midboss fight.
Person: long hair, red hair, sidelocks, red eyes, pointy ears, demon wings, head wings
Outfit: white shirt, collared shirt, juliet sleeves, long sleeves, black vest, red necktie, black skirt, skirt set, black dress, white legwear, socks, black footwear, mary janes