Yukiko Fujimine, who takes the surname Kudo upon marriage, is a retired actress internationally recognized for her role as Otome, Sakamoto Ryoma's older sister, in a historical drama. Her promising film career, initiated during her time at Teitan High School, concluded abruptly when she married mystery novelist Yusaku Kudo and left acting. Despite retirement, she retains connections in the entertainment world and earned the moniker "Night Baroness," inspired by one of Yusaku's literary characters. This title followed her inadvertent solving of a criminal case during a live television broadcast by revealing clues provided by her husband.

During her acting career, Yukiko trained under stage magician and disguise expert Toichi Kuroba to master disguise for a specific role. This training introduced her to actress Sharon Vineyard, sparking a close friendship. This bond endured until Sharon's purported death; Yukiko later uncovered Sharon's secret identity as the criminal organization member Vermouth, a revelation that deeply disturbed her. Yukiko confronted Vermouth to verify this truth and to protect Ai Haibara from the organization.

In the OVA "Aoyama Gōshō Tanpen-shū," specifically the segment "Ten Planets in the Night Sky," Yukiko searches for her missing husband, Yusaku, guided only by a cryptic message he left. Her infant son, Shinichi Kudo, unintentionally provides crucial hints through his behavior, including crying patterns and reactions to celestial references, aiding her in deciphering the message and locating Yusaku.

Yukiko exhibits perceptive and methodical thinking, often noticing details others miss. Her mastery of disguise allows her to convincingly adopt different identities, primarily female personas due to limitations in mimicking male voices. She is also an accomplished, though reckless, driver.