Seimei acts as a priestess of divination, astrologer, and yin-yang master dedicated to opposing the evil goddess Douma. She displays gray hair and red eyes. Her capabilities include summoning spirit beings, wielding magic scrolls for combat and rescues, and commanding minor goddesses like the dragon Seiryuu and turtle Genbu to battle demons.

Douma seized control of Japan through supernatural influence after intervening in the 1911 Yoshiwara fire. Seimei collaborates with detective Miyamoto Hiromasa and four minor goddesses—Byakko (Tiger), Seiryuu, Suzaku (Phoenix), and Genbu—to thwart Douma's schemes. During a mission to rescue a businessman from a spider-like demon spawned from Douma's hair, Seimei sustains a minor injury. Douma exploits this to curse her with uncontrollable sexual urges. The curse escalates rapidly, driving Seimei to intense masturbation and explicit demands for penetration to counter its life-draining effects.

Miyamoto volunteers to breach the energy barrier confining Seimei, ignoring warnings that transferring his sexual energy might kill him. Within the barrier, the curse and Douma's partial control compel Seimei into prolonged intercourse with Miyamoto. This act serves both as a curse manifestation and an attempted cure. Seimei exhibits heightened aggression, shedding her stoicism to taunt and physically dominate Miyamoto, draining his life force until he is exhausted.

Simultaneously, Seiryuu and Genbu assault Douma's Heaven Tower to aid Seimei and Miyamoto. They fail, are captured, violated by demons, and mentally broken. Their defeat weakens the containment barrier, intensifying Seimei's lust. Byakko later departs to join the fight against Douma, leaving Suzaku alone to sustain the barrier while Miyamoto continues satisfying Seimei's curse-driven demands. Seimei's curse and fate remain unresolved.