Japan might be famed for being a profoundly private society in which harmony with others is treasured above all else but this has not stopped Kazuyo Matsui from bearing the most intimate details of her private life on YouTube for the world to see.

The popular Japanese actress, who has been in showbusiness for 39 years, has released an emotionally fraught six-minute video accusing her husband of cheating on her.

Dressed in a black shirt and no make-up, Matsui reveals a slew of alleged secrets about her husband Eiichiro Funakoshi who is also a famous actor in the country.

“My husband and I have been married for 17 years,” Matsui told the camera. “However, I have found that my husband is having an affair with my best friend who lived in Hawaii. She is married and even has a daughter!”

Becoming visibly more emotional and raising her voice, Matsui then claimed Funakoshi has type-two diabetes and fake hair. It is virtually unprecedented to release details as intimate as one’s medical history and sexual habits in a country as starkly private and reserved as Japan.

She continued: “Therefore I’ve known that he could not have sex. However, I found out that he had been taking a 100-mg Viagra … Using Viagra he had been having sex with my best friend. I had trusted him”.

The actress, who starred in award-winning 1987 film A Taxing Woman, then went on to accuse her husband of being “after [her] money” together with her friend. She also claimed he has been trying to “tarnish” her reputation and has been leaking stories about her in Japanese tabloid magazines with the help and cooperation of his production agency.

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Matsui, who has been a mainstay on Japanese tabloid TV shows in recent weeks, said she had “cried for days” and even thought about taking her own life. Nevertheless, she said after turning 60 this year she had chosen to “fight against the dark shadows and [her] husband”.

The actress, who is also a businesswoman, added: “I’m fighting Japanese mass media. Newspaper, weekly magazines and TV programs have been talking about me for weeks now”.

It is not uncommon for men to have affairs in Japanese society, with the Japan Times arguing “adultery and infidelity are time-honored Japanese traditions for the nation’s men.”

While of course it is not wholly related to adultery, the male-centred sex industry makes up around two per cent of Japan’s gross domestic product. If a Japanese male is keen to have a sexual encounter, he has a vast array of options at his disposal, including sexual massage parlours, escort services, “soaplands” which are essentially licensed brothels, hostess clubs or myriad “meet-up” websites.

Nevertheless, this is not the case for women living in the country who have very few sexual services if they are seeking sex with no commitment.

Marriage in Japan is on the decline - a recent government report found nearly one in four men and one in seven women in Japan were yet to be married at age 50 in 2015.