Until then, he said, Japanese officials are trying to save them. Suga said his government will do its utmost to communicate with ISIS on the fate of Goto and Yukawa through a third party, such as another nation's government or a local tribe. He didn't say whether Japan would be willing to pay any ransom.
Absent such a private back-and-forth, the Japanese official voiced his government's stance publicly, including its defense of a proposed aid package, also tabbed at $200 million
, to help those who are "contending" with ISIS, according to Prime Minister Shinzo Abe
. Abe has defended the aid package as needed to build up "human capacities, infrastructure and so on," yet ISIS denounced it anyway in its recent video.
"Japan's measures are absolutely not intending to kill Muslim people, unlike what the hostage takers claim," Suga said Wednesday. "We strongly urge them not to harm the two Japanese nationals and immediately release them."
Friend: Hostage wanted to help Syrian rebels
Goto and Yukawa were last seen months ago, disappearing in the same part of the world. While they had different professions, the two knew and talked to each other, said Yukawa's friend Nobuo Kimoto.
It was January 2014 when Kimoto met Yukawa, who told him about his dream of providing security for Japanese ships in dangerous areas, such as waters off Somalia sometimes plagued by pirates. Three months later, Yukawa headed off to Syria to gain combat and survival experience, Kimoto said.
There, Yukawa met the man ISIS refers to as Kenji Goto Jogo (who goes by Kenji Goto on Twitter and in a photograph accredited to him). Goto is a freelance journalist who has worked for various Japanese news organizations, including reporting about the northern Syrian battleground city of Kobani
, which for weeks has been under siege by ISIS, and other areas.
Goto gave Yukawa insights on how to survive there, Kimoto said. He also introduced him to rebel fighters -- distinct from ISIS, even though both were fighting against Syrian President Bashar al-Assad
's forces -- some of whom talked about their need for ambulances to shuttle the injured. That plea spurred Yukawa to start raising money for this cause after returning to Japan, according to his friend 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."
He went back to Syria in July -- a trip that Kimoto said he didn't know about at the time. Kimoto said he had advised Yukawa to focus on building up his Private Military Company, which provided armed security services and posted videos online of his activities in Iraq and Syria.
Yukawa, 42, went missing and was captured sometime after that.
Goto met the same fate. While it's not known exactly when he became a hostage, his last Twitter post
was on October 23.
Fixer: Other hostage is a strong journalist
Alaaeddin Al Zaim worked as a fixer for Goto. Speaking to CNN in Turkey, he said the journalist had reached out to him about going into ISIS-controlled territory.
"I am not American, I am not British. I'm Japanese. I can go," Goto told the fixer. Fixers help reporters travel and connect with local contacts.
Al Zaim refused, believing the trip was too dangerous. Another fixer agreed to take Goto to ISIS, Al Zaim said.
Before he left, Goto made a short video -- which CNN saw -- in which he explained his decision to travel was his, and his alone. Goto gave Al Zaim his phones, and a list of numbers.
"He gave me this and asked me to call Japanese wife, his wife in Japan, his friends in Japan. After one week, if I don't hear any news of them or any connection, I have to call them," said Al Zaim, who remembers seeing Goto for the last time on October 25.
After a week, he said, he hadn't heard from Goto and so he made the call to his wife. Al Zaim, who described Goto as his brother, praised his reporting work.
"He is the best journalist I met him, and I work with him because he (doesn't) like military stories. He covered, every time, civilian and kids stories in Syria.
"And also he is very strong. Anytime he want to do his job very well ... Sometimes we are going to danger(ous) places, he (isn't) afraid. He tell(s) me: 'This is my job. I am journalist. I have to do that.'"
CNN could not immediately confirm the details of what Al Zaim said.
ISIS doesn't have a reputation for mercy
What happens next for both men is up to ISIS
. Unfortunately, it doesn't have a record of showing much mercy.
The Islamist militant group has been behind mass killings and kidnappings during its years-long campaign to take over vast swaths of Iraq and Syria, attempting to justify its actions -- like enslaving and having sex with young girls -- as somehow consistent with its extreme, conservative faith.
Taking hostages from outside countries has been part of its playbook. Not only has ISIS beheaded many of them, but it's made a show of it by recording their deaths and showing them online as propaganda, something that began in August with the killing of U.S. journalist James Foley.
Those beheaded hostages were American and British, both from countries involved in a military campaign against ISIS. Japan is allies with both, though it is not participating in any airstrikes or the training or outfitting of those fighting the militant group.
Tokyo's stance on the conflict, including the $200 million pledge that Abe made Sunday, was apparently enough to draw the ire of the group that calls itself the Islamic State.
"Although you are more than 8,500 kilometers away from the Islamic State, you willingly volunteered to take part in this crusade," said the masked man who stood over Goto and Yukawa in Tuesday's video, addressing his comments to Abe.
Abe has responded by defending the proposed aid and blasting ISIS' threat against two of his nation's citizens as "unacceptable."
"I feel angry about it," he said Tuesday. "I strongly urge them to immediately release the hostages without harming them."