User blog comment:Crimson and Darkness/Shin DxD 4 discussion/@comment-73.10.61.229-20200221000942/@comment-39047410-20200221001329

She's the girl from "Mysterious Girl". She's a human from FxF (Fadiru x Ferudora). Only info about her is that her name is Sefaira Seraselbas, she's from FxF, and she's a Fadiru Miko (Shrine Maiden). As for why her last name is Seraselbas, that's still unknown.