Fallen angel!verse/Demon!verse (sort of a subset of guardian angel!verse)
Known as Ariel Chein, the Lion of God’s Grace, Guinevere was once a guardian angel--one of many protector angels, each assigned respectively to a single soul, and that soul alone. An individual soul’s protector angel would guard their assigned soul through every life that soul lived, whether it was one or one million, until that soul fulfilled the purpose it was created for. Once their charge had fulfilled their purpose, the protector angel would return to the warmth of the Holy One, along with the soul they had protected. While she was one of many, the soul Ariel Chein was assigned to was most certainly not. Every soul is unique, but this soul was given a purpose that will keep it returning and returning until the End of Days and the Messianic War. Ariel Chein’s charge was King Arthur of Camelot, the Once and Future King.
Angels are meant to love. They are created for the purpose of loving God and Creation. Their love is not the same as a human’s love...but Ariel Chein fell in love with Arthur in a way she never expected to--and with every new life Arthur was born into, his protector fell exponentially more deeply in love with him. Until she stopped simply protecting him only to his assigned time of death and instead began attempting to extend his life past it. It never worked, and her essence slowly became corrupted with her grief at each new failure to protect and preserve her charge. Until that corruption consumed her, and so she was exiled.
Cast from the Heavens, Ariel Chein took the name Guinevere, after the woman who had been Arthur’s Queen in his first life, and she set out to finally fulfill her own purpose and protect the soul she so infinitely loves, using her corrupted essence as the means of this protection. Guinevere became a demon on par with the Four Demon Queens, and she will never back down until she has completed her task and saved Arthur.
She will destroy the world to save his life, and nothing in even the highest ranks of the Heavenly Hosts will stand in her way.
((OOC note: Judaism doesn’t believe in demons the way Christianity does. There are a specific number of fallen angels, but they aren’t really counted as demons, and there are no demons in Gehenna/Gehinnom (which isn’t really the same as Hell, but is similar), only punishing angels. So...this verse is very much a mix of Jewish and Christian theologies.))