Keiko Fukuda, the Japanese-born granddaughter of a samurai who learned judo from its founder and became the highest-ranked woman in the martial art, has died at age 99 in San Francisco, her friend and caregiver said on Saturday.

Fukuda died of natural causes at her home on Feb 9, said Shelley Fernandez, 82, who lived with Fukuda, helped her run the Soko Joshi Judo Club for women in San Francisco and referred to the woman as her adopted older sister.

Standing only 147 cm tall, Fukuda ventured into the fire-bombed streets of her native Tokyo during World War II to reach the dojo where she taught classes.

Fukoda continued to do judo exercises into her 90s, but used a wheelchair in her final years. At her dojo, she sat in a chair as her assistant teachers worked with students, and she would chime in with instructions, Fernandez said.

"Up until the last, she was very lucid and she never forgot any judo techniques - ever," said Fernandez, who added that Fukuda taught at the school three times a week until she died.

In July 2011, USA Judo conferred on Fukuda the rank of "10th dan", the highest level of mastery possible in the martial art.

She was the only woman in the world and the only person in the United States to ever achieve that status.

Only three others hold that title, and they are all men who received the promotion from the Kodokan Institute in Tokyo, which is considered the headquarters for the sport.

The Kodokan promoted Fukuda to "9th dan" in 2006, five years after she received that rank from the US-based branch of judo. The same year the Kodokan promoted her, it vaulted the three current male holders of "10th dan" to that level.

Fukuda was born in Tokyo on April 12, 1913, into an upper-class family.

Her grandfather was a samurai master of jujitsu who taught the martial art to Jigoro Kano, who went on to create judo. When Fukuda was 21, Kano invited her to join a women's division at the Kodokan.

As a woman, Fukuda had been expected to marry and devote herself to such home-based arts as the Japanese tea ceremony, but instead she gave herself over to judo. The decision was chronicled in a documentary film about her life called Mrs. Judo that has been on the festival circuit in recent months.

"That was my marriage," a tearful Fukuda said in Japanese in the film. "I chose judo over marriage. I never imagined I would live so long with this."

Female judo teachers in Japan were not allowed to marry, and Fukuda did not want to give up the sport, Fernandez said.

In another restriction placed on Fukuda because of her gender, she was barred from competing on the mat against an opponent, Fernandez said.

But she demonstrated judo techniques with a partner at the 1964 Olympics in Tokyo, the year judo was introduced as an Olympic sport.

Fukuda came to the United States in 1966 and became a US citizen six years later, founding her San Francisco-based school around 1970. Her motto for herself and those she taught was, "Be strong, be gentle, be beautiful."

"Judo, it's not just a sport, it's a mental, physical and spiritual centering of your life, and it's an art and a science as well, and her life was totally in balance," Fernandez said.

Reuters