On Tuesday, ISIS released a video threatening to kill the two men -- Kenji Goto and Haruna Yukawa -- unless Japan paid the group $200 million within 72 hours.
Based on the time frame, the Japanese government estimated that the ultimatum expired at 2:50 p.m. Friday, Tokyo time (12:50 a.m. ET Friday), and scrambled to secure the men's release.
Hours before the estimated deadline, an ISIS spokesman told Japanese broadcaster NHK that the group would release a statement "soon" about the hostages. That statement didn't come.
When asked whether ISIS has been in negotiations with the Japanese government, the spokesman told NHK he wouldn't comment.
ISIS claims the ransom amount is the same as the financial aid pledged by Japanese Prime Minister Shinzo Abe
to countries affected by the militant group.
Japanese officials have repeatedly stressed that their military, which is constitutionally forbidden from taking action other than for self-defense, isn't involved in the international airstrikes against ISIS positions in Syria and Iraq. The Abe pledge is for humanitarian purposes, like helping refugees, not military purposes, Japan says.
But ISIS appears unswayed.
In his communication with NHK, the ISIS spokesman said the group is aware of what Japan says -- and then he went on to call the Japanese infidels for fighting with the group.
Tokyo faces a dire predicament.
It says it's doing its best to communicate with ISIS. It wants to secure the hostages' safe release, but it won't yield to threats.
Japanese Chief Cabinet Secretary Yoshihide Suga said he was aware of reports that ISIS would soon make a statement.
"We are receiving many different pieces of information, but as a government, we cannot really comment as to whether that information is authentic," he said.
Caught in the middle
Caught in the middle are the two men, Goto and Yukawa.
As the apparent deadline approached, Goto's mother begged for her son's life.
"To all members of ISIS, Kenji is not the enemy of ISIS. Please release him," said the mother, Junko Ishido. "There is so little time left before the deadline."
"I have been just crying for the last three days, filled with sadness. Words fail to describe how I feel. Kenji always has been a kind person ever since he was little. He was always saying, 'I want to save the lives of children in war zones.' "
Leading Japanese news organizations have reported, citing unidentified government sources, that Goto's wife got an email in December from someone demanding $8 million to $16 million for her husband's return.
The government is trying to confirm if that email came from ISIS, the reports said. If so, it could indicate the militant group is willing to accept a smaller ransom than the $200 million it had publicly demanded.
But the question is what, if anything, Japan
is willing to give.
ISIS has a ruthless track record. It has released videos touting the killing of five Western hostages since August.
Abe has called ISIS' ultimatum over the two Japanese men's lives "unacceptable" and said the international community shouldn't give in to terrorists.
But he and other government officials haven't explicitly ruled out paying a ransom.
A veteran journalist
Some details have emerged about what spurred the two Japanese citizens to travel thousands of miles to the bloody Syrian conflict
. While they had different professions, the two men knew and talked to each other, said Yukawa's friend Nobuo Kimoto.
Goto, an experienced freelance journalist, made a video in October near the Turkish-Syrian border before he embarked on a perilous journey into ISIS-controlled territory.
"It is my responsibility if something happens," he explained.
Goto, 47, said he was determined to cover what was happening in the region.
"Syrian people suffering three years and a half. It's enough," he said. "So I would like to get the story of what ISIS
wants to do."
Alaaeddin Al Zaim, who had worked with Goto in Syria previously, says he warned him not to enter the ISIS stronghold of Raqqa. "I tell him it's not safe for you," Al Zaim told CNN.
But Goto chose to go anyway, saying, "I am not American, I am not British. I'm Japanese. I can go," Al Zaim recalled.
An aspiring security contractor
The aims and activities in Syria of Yukawa, a 42-year-old unemployed widower, are murkier.
He originally headed to the war-ravaged country early last year with the aim of gaining combat and survival experience to bolster his plans to set up a private security company, said his friend Kimoto.
There, Yukawa met Goto, who gave him insights on how to survive there, Kimoto said. He also introduced him to rebel fighters, who are distinct from ISIS even though both are fighting against Syrian President Bashar al-Assad
Some of the rebels talked about their need for ambulances to shuttle the wounded. That plea spurred Yukawa to start raising money for this cause after returning to Japan, according to Kimoto.
"I felt a chill when he said, after returning home, (that) he felt in Syria he was really living a life," Kimoto said. "He seems to have felt satisfaction being there and living together with the locals."
Yukawa went back to Syria in July, a trip that Kimoto said he didn't know about at the time. Kimoto said he had advised his friend to focus on building up his private security company.
Yukawa was reportedly captured in August.