This character had initially no official name. Fans have named her "Koakuma", meaning "Little Devil" or "Imp". ZUN later confirmed this name in an interview, though.
In a cameo appearance in Inaba of the Moon & Inaba of the Earth chapter 23, she is depicted with two pairs of black wings, one on her head and one on her back. In this cameo she is also seen cooking and flipping Okonomiyaki at a beach stand that's also selling ramen and Yakisoba... in the middle of what appears to be rows of books in a library. Tying into Silent Sinner in Blue, the location of this stand was the swimming pool at Patchouli's library (Remilia's "Indoor Sea"). She has another cameo in Strange and Bright Nature Deity chapter 14, where she once again has the black wings on both her head and her back, and appears to be serving Patchouli in the library.
In one of EoSD's sprite sheets, it shows Koakuma with magenta hair and a magenta aura. It is possibly an unused sprite for the extra stage, as she stands by the extra stage sprite of Patchouli.
Her bat wings on her head and back, are similar to Morrigan's from the Darkstalkers/Vampire games. This has made many fans believe she might be a Succubus.