Setsuko, Princess Chichibu (雍仁親王妃勢津子, Yasuhito Shinnōhi Setsuko, born Setsuko Matsudaira (松平節子, Matsudaira Setsuko); 9 September 1909 – 25 August 1995) was a member of the Japanese imperial family and the wife of Yasuhito, Prince Chichibu, the second son of Emperor Taishō and Empress Teimei. Setsuko was a sister-in-law of Emperor Shōwa and an aunt by marriage of Emperor Akihito.

Setsuko Matsudaira was born on 9 September 1909 in Walton-on-Thames, England, into the prominent Matsudaira family.^[1][2] Her father, Tsuneo Matsudaira, was a diplomat and politician who later served as the Japanese ambassador to the United States (1924) and later to United Kingdom (1928), and still later, Imperial Household Minister (1936–45, 1946–47). Her mother, Nobuko Nabeshima, was a member of the Nabeshima family. Her paternal grandfather, Katamori Matsudaira, was the last daimyō of the Aizu Domain and head of the Aizu-Matsudaira cadet branch of the Tokugawa. Her maternal grandfather, Marquis Naohiro Nabeshima, was the former daimyō of the Saga Domain. Her mother's elder sister, Itsuko (1882–1976), married Prince Morimasa Nashimoto, an uncle of Empress Kōjun. Despite her prestigious heritage, Setsuko was technically born a commoner, but both sides of her family maintained kinship with distinguished kazoku aristocratic families close to the Japanese Imperial Family.

From 1925 to 1928, Setsuko was educated at the Sidwell Friends School in Washington, D.C. while her father was ambassador to the United States.^[3] Setsuko was fluent in English and was sometimes considered to be a Kikokushijo. Upon her return to Japan, Setsuko was chosen by Empress Teimei to marry her second son, Yasuhito, Prince Chichibu, despite the fact she was a commoner.^[4] Setsuko married the Prince after her uncle, Viscount Morio Matsudaira, formally adopted her, thus removing the status incongruity between the prince and his bride.^[5]

On 28 September 1928, aged 19, Setsuko wed Prince Chichibu, and became Princess Chichibu.^[6][7][8] The bride and groom were eighth cousins, thrice removed, as both were descended from Nabeshima Katsushige, the first lord of Saga.^[9] Prince and Princess Chichibu had no children, as Princess Chichibu's only pregnancy ended in a miscarriage. However, by all accounts their marriage was filled with love and happiness for each other.^[10][11]

In 1937, the prince and princess were sent on a tour of Western Europe which took several months.^[10] They represented Japan at the May 1937 coronation of King George VI and Queen Elizabeth in Westminster Abbey and subsequently visited Sweden and the Netherlands as the guests of King Gustav V and Queen Wilhelmina, respectively. Princess Chichibu stayed in Switzerland while her husband met Adolf Hitler in Nuremberg at the end of the trip.^[12] Princess Chichibu felt a great love for the United States and for England and, as an anglophile, was greatly saddened by Japan's entry into the Second World War on the side of the Axis powers.^[13][14]

After the Prince's death of tuberculosis in 1953,^[15] Princess Chichibu became president of the Society for the Prevention of Tuberculosis, honorary president of the Britain-Japan Society, the Sweden-Japan Society, and an honorary vice president of the Japanese Red Cross^[16] The Princess made several semi-official visits to Great Britain and Sweden.

Princess Chichibu died from heart failure in Tokyo on 25 August 1995, shortly before her 86th birthday.^[17][18] Princess Chichibu's autobiography, which was published posthumously as The Silver Drum: A Japanese Imperial Memoir, was translated into English by Dorothy Britton.^[19]

• Grand Cordon of the Order of the Precious Crown, 1st Class - 1928^[8]
•  United Kingdom: Dame Grand Cross of the Most Distinguished Order of Saint Michael and Saint George