She would befriend the elderly men through a matchmaking agency, usually going for those who are childless and well-to-do.
When they trusted her enough to make her the sole beneficiary of their assets, Chisako Kakehi would move in for the kill - like the venomous black widow spider that devours its partner after copulation.
The 70-year-old, dubbed "Black Widow" by Japan's media, was yesterday convicted and sentenced to death by a Kyoto court for the murders of three lovers and attempted murder of an acquaintance.
She was expressionless as the verdict was read out in a hearing yesterday, local media reported. Her lawyers have filed an appeal against what they call an "unjust" verdict.
The prosecution said that Kakehi had pocketed at least 1 billion yen (S$12 million) from life insurance and inheritance payouts between 2007 and 2013.
Like the spider she is named after, she delivered death by poison - getting the men to down cyanide passed off as a health cocktail.
Among them was her fourth husband Isao Kakehi, 75, whose marriage to her after being widowed for a long time aroused police suspicions. He died on Dec 28, 2013, only a month after their marriage.
She was also accused of killing her common-law partners Masanori Honda, 71, and Minoru Hioki, 75, and for attempting to murder acquaintance Toshiaki Suehiro, 79. Three other men romantically linked to her had also died, although she was not charged for their deaths.
The Kitakyushu-born Kakehi first got married at 24 to a former truck driver. They later started a T-shirt printing business in Osaka.
Her first husband died in 1994 and the business later went bust, prompting her to take out massive loans. His death had not been seen as suspicious but was the first of many eventually linked to her.
Kakehi has lamented her lot in life to reporters and insisted she is the victim of unfortunate events.
The prosecution's case rested on a small bag of cyanide found in a plant pot that Kakehi had tried to discard. They accused her of plotting her crimes well in advance, including helping to prepare notary documents linked to wills.
But the defence argued that much of the case rested on circumstantial evidence, and there was no evidence directly pinning Kakehi to the deaths - including how she had obtained and stored the cyanide.
They added that legal autopsies have not been performed on some of the victims, and Kakehi, who has early onset dementia, was not a reliable witness in the 135-day trial.
She had stunned the nation in July with an open confession. "I killed my husband. I have no intention of hiding the guilt. I will laugh it off and die if I am sentenced to death tomorrow," she was reported as saying. But she quickly retracted her confession.
A court-appointed physician said last year that Kakehi's case of dementia was mild and that she was fit to stand trial.
Yesterday, presiding judge Akiko Nakagawa said: "It was an extremely malicious and shrewd crime borne only out of a greed for money."