She is voiced by Satomi Satō.
Ryukotsuki is a demon from a distant hell, one of Hanafuuma's most dangerous enemies and the last boss on Getsu Fūma Den. Ryukotsuki was resurrected by the Gofer Sisters so they could employ her power against the "G" Organization.
Her loyalty is maintained through her personal honor and an invoiced bill for the price of resurrecting her. The amount is ludicrous, and intentionally designed to take a long time to pay off. Occasionally, Ryukotsuki attempts to gamble to lower her debt, although it usually goes badly. She pilots the Serpent Core.