Sayako, who had insisted for years she would wait to marry, walked several steps behind the groom to a specially built Shinto altar in a prestigious Tokyo hotel on Tuesday in a reverse fairy-tale that has been closely followed across Japan.
Wearing a simple Western-style white dress and a single-strand pearl necklace, Sayako exchanged vows and shared a ceremonial glass of sake wine with Yoshiki Kuroda, a 40-year-old urban planner.
Sayako quit her job as a part-time bird researcher and, under a now-controversial tradition, loses her imperial status by marrying a commoner.
She acknowledged she had only a remote idea about her new life in a rented home in middle-class Tokyo.
"I was very glad that the emperor and empress think that this new life is not a total change but an extension of my life so far," Sayako said in a five-minute news conference with her new husband.
"I would like to start a new life as a member of the Kuroda family by learning various things," she said.
Her husband said: "While respecting each other's views, I would like to make a quiet home where you can feel at ease."
The princess is the first Japanese royal woman in modern times to wed in her 30s.
It mirrors the trend in Japan, which is struggling to counter a declining birthrate as more young people choose to put off families for the sake of careers and lifestyles.
Japanese Emperor Akihito (L)
and Empress Michiko
The wedding was not accompanied by the grand, public ceremonies seen for former career diplomat Masako Owada's wedding to Crown Prince Naruhito in 1993.
The former princess later put on a kimono once worn by her mother and attended a champagne reception with 150 guests, including Emperor Akihito and Empress Michiko, who broke tradition by attending their daughter's wedding reception.
In the morning, thousands of well-wishers lined the roads and royal minders bowed deeply as the princess was driven off in a black limousine from the palace to the nearby Imperial Hotel.
"Many people feel close to the princess because she is descending to a commoner's rank," said Hiroshi Inamura, 68, who camped out all night to be the first to write his name in the congratulatory book.
The groom, Yoshiki Kuroda, is an
Crown Princess Masako, who has shunned the public eye for almost two years due to stress, showed up to see off her sister-in-law, who entered the Shinto-style ceremony holding a fan with a tuft.
Masako has been under intense pressure to produce a male heir to the Chrysanthemum Throne because her only child, three-year-old Princess Aiko, under current rules cannot become Japan's monarch.
The male-only succession rules also mean Sayako must leave the imperial family, becoming "Mrs Kuroda" upon her marriage to the metropolitan government employee, who was a childhood friend of her brother.
As no boy has been born to the royal family since 1965, Japan is studying allowing women to assume the throne and letting princesses keep their royal status after marriage. But any change would come too late for Sayako.
Sayako is the youngest child of Akihito and Michiko and the last of their three children to wed.
She has been preparing for her new life by learning everything from how to drive to how to sort out the rubbish. But her transition was eased by a one-time government payment of $1.3 million as an allowance for becoming a commoner.
Michiko, who was the first commoner to marry into the monarchy, last month recalled how Sayako supported her mother whenever she was disappointed.
Noting that Akihito calls the princess "our Miss Don't Mind," the empress said in a statement: "How fondly we will remember and miss this tender and heart-warming 'Don't mind' in the days to come."