Peony was a courtesan who worked on Nagasaki. She was a suspect in the murder of Director Jan Spaen in "The Way of the Traitor". To the outside eye, Peony was the perfect suspect due to the fact that she was mistreated by Jan Spaen in front of others. Sano Ichirō went to the Half Moon Pleasure House in Nagasaki to question Peony, and found her being mistreated by the courtesans who were higher up on the totem pole then herself. When Sano sees her, he observes a woman in her twenties wearing a plain blue cotton kimono and a large puffy face, with her only saving grace being her blue black hair. When Sano approaches her, he is also accosted by the proprietor, Minami Hideo. After being told he is looking for Peony, Minami calls her over, then discovers that Peony has taken a silk fan from one of the courtesans she was waiting on. Minami then beats her and drags her to an empty room where she can be questioned by Sano. Peony reveals to Sano that the way Jan Spaen treated her was all a game, a primitive form of what is now referred to as S&M. Sano attempts to get her confess to murdering and shooting Spaen, but Peony insists that she loved Spaen and would never have wanted to hurt him. She tells Sano that she was not the only person admitted to the island of Deshima the night of Spaen's murder. Another person, Urabe, was admitted as well.
After Sano goes, Peony goes to the privy and takes out a black laquer box, where she stores her stolen treasures. As she caresses the box, she remembers the past, including the first time she stole, which was a beautiful doll from a toy peddler. Eventually, though, Peony's thieving ways caught up with her. One day as she worked in a rich man's house at the age of fourteen, she took some bridal ornaments from the bride on her wedding day and put them in her own hair. Upon the bride seeing them and crying "Thief!", Peony was arrested and taken before the magistrate, who sentenced her to work in the pleasure quarter of Nagasaki until she had earned enough money to pay back what she had stolen. She was forced to work at the Half Moon Pleasure House under Minami's supervision, suffering beatings and humiliations, including exposing her most private parts to clients while dancing. She was then sentenced by Minami to service the Dutchmen in Deshima. Peony tried to drown herself rather then suffer such humiliation, but was saved and forced into the room of Jan Spaen. Upon entering and introducing herself to Spaen, she soon discovered that Spaen liked to be tortured during sex by his lovers, including being tied to a chair and flogged. Peony participated in this, and soon learned that Spaen also liked to humiliate his lovers in turn so his arousal is more pronounced. Despite feeling sad over his death, she felt joy as well for him getting what he deserved for the way he had treated her.
Peony then gets a messenger to deliver a message for her to an unspecified someone, that she has something for them in return for ten thousand koban. The messenger goes to deliver the message while Peony returns to work. Later, around the hour of the boar, she is waiting nervously for the person she sent the message to to arrive. Getting nervous, she goes to a room, takes out the laquer box, a comb, and a mirror, and began to comb her hair. She begins to daydream about leaving the brothel and living a life of luxury and elegance when her guest arrives with a cloth bundle under his arm. Peony is excited thinking it is the money she requested, but is horrified to see a knife instead. She pleads with the attacker to take whatever is in the box and go, but the attacker slashes her neck open and kills her. Later, Sano is called to the brothel where she has been discovered, and he finds a suicide note near her body. But Sano does not believe she caused her own death.
Later, it was revealed that what Peony had in her possession the account book of Iishino, which contained records of stolen and smuggled goods onto the island. Iishino had killed Peony to prevent her from bringing the information forward.