In a purple and gold kimono and with her hair swept back, 77-year-old Kazuko Tsuji says she called the man who was toppled from power by the Lockheed scandal oto-san, the respectful Japanese term for father, but Tanaka never gave her any presents during their 47-year relationship and was "very quick to raise his hand".
And while these intimate details of the life of one of Japan's most powerful leaders would have been carried to a geisha's grave in the past, Tsuji believes Tanaka would approve of a book that has shot to the top of the bestsellers list.
More than 100,000 copies have been snapped up in the four weeks since Passion: The Geisha Who Captured Tanaka hit store shelves, publisher Kodansha says.
"When I decided to write the book, I was quite ill and it is 11 years now since he passed away," Tsuji said. "I wanted to leave something of myself behind and I wanted to present a different image of father.
"Is it so wrong for me to tell my story? I think father is applauding and is overjoyed that I wrote the book."
Quite whether he would be so keen for the book to sell so well will never be answered. Tanaka died in December 1993 while still trying to reverse his conviction for corruption in the worst scandal to shake Japanese politics since the second world war.
Tsuji appears with Tanaka on the
front cover of her autobiography
Neither his wife nor his daughter Makiko Tanaka, who has followed in her father's footsteps and is an outspoken independent politician, have commented on the book's publication.
One of the country's most powerful politicians in the 1960s and 70s, Tanaka had the highest popularity rating of any Japanese prime minister in history when elected in 1972.
He normalised relations with China that year, arranged enormous investment in the national railway system and was respected by the electorate for his dynamism.
Despite being arrested in 1976 for taking a Y500 million bribe ($4.7 million) from Lockheed in return for a huge defence contract, Tanaka continued to exercise influence over subsequent Liberal Democratic Party administrations.
By the time he was arrested, Tsuji had been his mistress for three decades and borne him two sons, Kyo and Yu, but she says his persona at home was very different from his public image.
"When [Tanaka] came home, he had no facades, no pretences"
former geisha of late Japanese prime minister Kakuei Tanaka
"When he came home, he had no facades, no pretences, but he was much more aware of things than I was," Tsuji said in her tiny, halting voice.
"I was drawn to father because of his great kindness and our relationship was very clean in terms of money.
"I was not fond of luxurious things and father never bought me any jewellery. I think that austere kind of life made him happy," Tsuji said of Tanaka.
"I still believe that he was very clean with finances," she said, defending a man considered by many to have been the most corrupt politician in Japanese history.
"I have heard the rumours but I only know what I saw and I believe that he was a very clean man financially," Tsuji said.
He was a "traditional Japanese man" in many ways, she said, demanding that children be respectful of their elders and that women remain quiet and in the background.
"We fought quite often and he was very quick to raise his hand. I saw sparks one time because he hit me so hard, and the next day it would all be forgotten. But he never once apologised."
Tanaka in October 1974, shortly
before he resigned as premier
Tsuji's revelations will shock older generations of conservative Japanese - as will the fact that a woman from the traditionally closed "floating world" has actually gone ahead with a kiss-and-tell expose.
There has always been a fascination outside Japan with the white-painted faces, elaborate kimonos and delicate turtle-shell hair ornaments - rejuvenated in recent years by Arthur Golden's fiction-based-on-fact Memoirs of a Geisha - enhanced by a code of silence within the narrow confines of their world.
But it appears that the secret trysts of Japan's most rich and influential men may no longer remain that way.
Under the spotlight
In August 1989 - after a little more than two months in office - then prime minister Sosuke Uno was forced to resign amid a sex scandal revealed by a geisha who claimed that he would not support her with an amount that she considered appropriate.
Japan's changing political culture
no longer has place for geishas
The domestic media largely ignored Mitsuko Nakanishi's indignation, until the Washington Post picked up the story and put Uno in the spotlight.
And while that affair faded in the memory as fast as Uno's political career, Japan's tabloid media have been having a field day recently as another politician's mistress has bared all.
"It is true that I was [Taku] Yamasaki's lover, but I can never forgive him for forcing me to abort his babies, telling me that sex becomes better after abortions, or for forcing me to have perverted sex with him," Kanako Yamada charged in the Shukan Gendai weekly magazine.
Yamada's anger has been provoked by Prime Minister Junichiro Koizumi's appointment of Yamasaki as his own special assistant, despite a stream of allegations concerning his philandering in the run-up to last November's Diet elections.
In his southern Japan stronghold of Fukuoka, from where his constituents had returned him for 30 years, he was soundly beaten after the former bar hostess told a press conference that she had been Yamasaki's mistress for 10 years until November 2001.
Tsuji's motivation for going public with her experiences, however, are very different.
"I thought about writing a book many times over the years because I felt that the world I inhabited is shrinking," Tsuji said.
"The geisha, the restaurants and the people who know that world are all becoming fewer and fewer, and my memories are also beginning to dim."
"The geisha, the restaurants and the people who know that world are all becoming fewer and fewer, and my memories are also beginning to dim"
And although she may deny that she is resentful of Tanaka refusing to allow her sons to see their father after he was incapacitated with a stroke in 1985 or to attend his funeral, there is disappointment not far below the surface.
"It may be difficult for some people to understand but it was through fate that I met Tanaka," she said. "He had a wife and children already but I felt a strong connection and that I wanted to do something to help him. I hope that Makiko can hear that."