小悪魔  (Character)

Koakuma (小悪魔) is a devil where she's seen around the library of Scarlet Devil Mansion where she apparently lives in the mansion. Her exact role is difficult to tell, but she is believed to be an assistant in Patchouli Knowledge's library. She was the fourth stage midboss of Embodiment of Scarlet Devil and little is known about her, and unless she makes another appearance, she remains a mystery.
* from Touhou Wiki