Over the past 15 years, Satoru and Naomi Abe have visited about 180 people across the country, interviewing them about their homemade bento.
They include an experienced ama female diver on the Boso Peninsula, a popular masked professional wrestler in the Kansai region and a chief brewer of sweet potato shochu liquor in Kagoshima Prefecture.
In their quest for homemade bento, the couple would pore over a map of Japan and call workplaces in the cities they are interested in, asking, "Is there anyone who brings bento?"
Freelance photographer Satoru recalled that about 15 years ago he had the random thought that he would like to take a peek into other people's bento. That was the beginning of a collaboration with his wife, Naomi, who was then an aspiring writer.
Many of those they spoke to modestly demurred at first: "Mine is just an ordinary bento." But conversations with such people often develop into sharing memories of their mothers' home cooking, their work and even life itself.
A man who works in a cattle barn in Gunma Prefecture brings a single gigantic rice ball, which he prepares himself.
As he leaves the house early in the morning, he does not want to ask his wife to make his lunch. He takes big bites of his rice ball when time allows at work.
"From their bento, we can tell what kind of person they are and also their lifestyle at home," Naomi said.
Satoru, 51, and Naomi, 44, married in 1998 after they met through a mutual friend. They work from a home office in Tokyo.
Their photo book "Obento no Jikan" (Time for bento) has earned such acclaim that a third edition will be published in March.
The couple have become known as "bento hunters."
Their search continues today, as they ask more people around Japan for a thrilling peek under the lids of their bento boxes.