Bursting onto the international scene aged 15 with a Fukuoka Cup victory against four-time world champion Karen Briggs, the Japanese star went on to dominate the extra-lightweight category (-48kg) for two decades.
Tani is the first female judoka in history to compete at five Olympic games and the only one to walk away with a medal on every occasion.
She went a remarkable 12 years unbeaten at international level, winning every major competition she entered from the end of 1996 to 2008.
"I feel very fortunate," Tani tells CNN Sport in an exclusive interview, donning her judogi for the first time in "at least five years," having retired from judo in 2010.
"Strangely I did not feel much pressure when I was competing, but this was because I was training very hard every day, and I knew I was the most well-prepared for the competition."
"I feel most comfortable in my judogi and on the mat -- especially with the medals in front of me."
Japan may be the traditional heartland of judo, but that hasn't always been the case for women.
As a young girl, Tani had to overcome the resistance of her mother, who would have preferred her to take lessons in something "more fitting"
such as tennis or the piano.
Her determination certainly paid off.
Taking to the tatami for the first time aged seven, Tani won her first judo title just a year later -- defeating several boys along the way.
"My first big memory was of course my first gold medal I won when I was eight years old," she says with a smile.
"This was the first time I'd worked really hard for something and it materialized. This was when I realized that I had a real passion for judo, and that I really wanted to win."
When women's judo made its official Olympic bow at Barcelona 1992 -- 28 years after the men's competition -- Tani thrilled crowds on the way to reaching the final aged just 16, only going down to French world champion Cecile Nowak.
The young star promptly won her first World Championship gold the following year in Canada, a feat she repeated on home soil in 1995.
The stars were aligned for her to become Japan's first ever women's Olympic gold medalist at Atlanta 1996, but Tani once again had to be content with silver, this time losing to Kye Sun-hui of North Korea.
"Before the Sydney Olympic games I fought at two Olympics," she recalls. "I was the undisputed favorite to win, but I was unable to achieve the gold medal."
The Japanese hotshot had a motto -- "minimum gold, maximum gold" -- that summed up her single-minded approach.
No wonder she made it third time lucky at Sydney 2000, defeating Russia's Lioubov Brouletova to seal the only title that had eluded her.
"It was always my dream since I won my first gold medal aged eight to one day win the Olympic Games," she says. "So achieving this at the Olympic games was a truly special moment."
Now well into her stride, Tani swept aside all rivals at every major championship -- held biennially -- for over a decade.
For Tani, two of those victories are particularly memorable.
"In Athens in 2003, I was married and my name changed from Tamura to Tani," she recalls. "I wanted to prove I had the capability of winning a gold medal even after I was married, so that was extremely significant.
"And the 2007 world championships in Rio was truly special because in 2005 I gave birth to my first child.
"Two years later I was able to come back from childbirth and win the gold medal. This was very special to me."
Sports meets politics
Not content with gold medals in seven World Championships and two Olympic Games, the Japanese hotshot moved into politics upon her retirement.
"I was very interested in politics from a very young age," says Tani. "From as early as high school in fact.
"Through judo I traveled to many cities and countries. And I've seen the power of sport. I have realized that sport is a backbone in the structure of governments around the world.
"The main premise of myself becoming a politician after retiring as an athlete was to aid in sport development, because I know how much sport can come to the aid of people.
"With the 2020 Olympic games and Paralympic games coming up, I really wish to contribute to the development and proliferation of sport. Not only in Japan, but throughout the world."