O-Sayumi is the daughter of the pearl merchant and wizard Yugureda Shosaito and a lady of humble origins named Kaori. When Yugureda decided to have Kaori killed to arrange a more advantageous marriage for himself, Kaori fled into the nearby swamp, but Yugureda’s nue cohort chased her down and killed her. Before she died, however, Kaori managed to hide her daughter in the swamp, where she was found by the wise kappa Numataro-sama. The kappa raised O-Sayumi as his own daughter until he finally gave her into the care of monks of Irori. O-Sayumi learned to play the samisen in the orphanage, and when she was older, she left the monastery and began training to become a geisha in the Kiniro Kyomai teahouse, an elegant building with shiny brass gutters in the entertainment district of Sakakabe.

O-Sayumi is a master of traditional geisha skills, including song, classical music, dance, song, and the tea ceremony. O-Sayumi is a virtuoso performer on the samisen, and is also an accomplished practitioner of the geisha fan dance, which she has modified into her personal fighting style. Her weapons are two folding fighting fans that she normally carries in her sash. O-Sayumi loathes violence, however, and fights only in self-defense.

A beautiful young woman in her early twenties, O-Sayumi bears a striking resemblance to her mother Kaori. With her noble features, jet-black hair, and slender body, O-Sayumi cuts a stunning figure. An epitome of the geisha spirit, O-Sayumi believes in peace and goodness, and is exquisitely mannered and gentle.