Prime Minister Shinzo Abe promised Sunday “to make the terrorists pay the price.” Credit Toru Hanai/Reuters

TOKYO — When Islamic State militants posted a video over the weekend showing the grisly killing of a Japanese journalist, Prime Minister Shinzo Abe reacted with outrage, promising “to make the terrorists pay the price.”

Such vows of retribution may be common in the West when leaders face extremist violence, but they have been unheard of in confrontation-averse Japan — until now. The prime minister’s call for revenge after the killings of the journalist, Kenji Goto, and another hostage, Haruna Yukawa, raised eyebrows even in the military establishment, adding to a growing awareness here that the crisis could be a watershed for this long pacifist country.

“Japan has not seen this Western-style expression in its diplomacy before,” Akihisa Nagashima, a former vice minister of defense, wrote on Twitter. “Does he intend to give Japan the capability to back up his words?”

As the 12-day hostage crisis came to a grim conclusion with the killing of Mr. Goto, the world has suddenly begun to look like a much more dangerous place to a peaceful and prosperous nation that had long seen itself as immune to the sorts of violence faced by the United States and its Western allies.

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Some described a level of shock not unlike that experienced by the Americans after the 2001 terrorist attacks, or the French after last month’s assault on the newspaper Charlie Hebdo and the murders in a kosher supermarket.

“This is 9/11 for Japan,” said Kunihiko Miyake, a former high-ranking Japanese diplomat who has advised Mr. Abe on foreign affairs. “It is time for Japan to stop daydreaming that its good will and noble intentions would be enough to shield it from the dangerous world out there. Americans have faced this harsh reality, the French have faced it, and now we are, too.”

The crisis also comes at a crucial moment in Japan’s modern history. Since taking office two years ago, Mr. Abe, a strong-willed conservative, has tried to push his nation into shedding the passive brand of pacifism that it repentantly embraced after defeat in World War II, and playing a more active role in world events. Analysts and former diplomats say the stark savagery of the killings will be an important test of how ready Japan really is to step onto the global stage.

The question, analysts and diplomats say, is whether the trauma of the killings will drain Japan’s will to seek a higher international profile, or stiffen its resolve.

This new challenge came in the form of two videos released within a week of each other, both by the Islamic State, whose militants control large parts of Syria and Iraq. The first video, posted online last weekend, showed the decapitated body of Mr. Yukawa, 42, an adventurer who was captured last August by the Islamic State, also known as ISIS or ISIL. The second video, which surfaced over the weekend, showed the doomed journalist, Mr. Goto, 47, stoically kneeling as his dagger-wielding executioner criticizes Japan for joining the American-led coalition against the Islamic State.

He then menacingly warns that no Japanese are safe anywhere in the world.

“Let the nightmare for Japan begin,” the masked militant proclaims before reaching down to kill Mr. Goto.

Japan reacted with an outpouring of fury and sorrow at the death of Mr. Goto, a respected journalist who was a veteran of war zones. Local television stations showed clips from his reports from places like Syria and Iraq, where he often reported on the plight of children and noncombatants. It was also noted that Japan was not even involved in the United States-led bombing campaign against the Islamic State, but its citizens were taken hostage and killed in the same cruel manner as those from other countries.

“I feel a deep despair that I’ve never felt before and an unfocused anger,” Taku Nishimae, a filmmaker who began an online campaign to free Mr. Goto by holding up a placard saying “I am Kenji,” told Kyodo News.

For now at least, such anger appears to have given Japan the resolve to reject the Islamic State’s threats, and to support Mr. Abe’s efforts to raise Japan’s profile in the Middle East.

At the same time, many Japanese also appeared ready to adapt to this new reality by discussing ways to reduce their nation’s vulnerability. On Japan’s Sunday morning political debate programs, politicians seemed to compete with one another in offering proposals to increase security, by such steps as more screening of foreigners entering the country, creating an overseas spy agency or writing new legislation to give Japan’s tightly constrained military more freedom to act overseas to protect the more than 1.5 million Japanese who live abroad.

“I don’t see any sign of the Japanese people wanting to back down; to the contrary, they are quite angry,” said Ichiro Fujisaki, a former Japanese ambassador to the United States. “It’s actually surprising the extent to which people are united in standing against the terrorist group.”

Other analysts agree that the Japanese public seems to be rallying around its leaders in a time of crisis. They added, however, that as the shock wears off, there will be more questioning of how Mr. Abe’s government handled the crisis. In particular, they expect growing attention on how much responsibility Mr. Abe should bear for creating the crisis in the first place.

“The debate starts from now,” said Fumiaki Kubo, a political expert at the University of Tokyo. “Opinions were divided before the hostage crisis, but they may prove even more divided after it.”

Critics on the left are already starting to fault Mr. Abe for provoking the Islamic State two weeks ago when he offered $200 million in nonlethal aid to countries that were confronting the group. In its initial ransom demand, the Islamic State made a point of demanding the same sum, $200 million, and later criticizing Mr. Abe for what it called his “reckless decision to take part in an unwinnable war” waged by the United States-led coalition against the militant group.

This has already been enough to renew fears among many Japanese that Mr. Abe’s efforts to raise Japan’s profile could end up entangling the country in distant wars. These concerns were apparent on Sunday in interviews with citizens on their views of Japan’s response to the hostage crisis.

Hiroyuki Hamada, 61, an engineer who lives in a Tokyo suburb, said he was opposed to getting any more deeply involved in the United States-led effort against the Islamic State.

“I fear we will just fall into an unending cycle of violence begetting violence,” Mr. Hamada said.

But there have also been strong popular shows of support for Mr. Abe and his efforts to make Japan a more global partner of the United States, on whom it still relies for its defense. In coming weeks, Mr. Abe will seek legislative changes to expand the role of the military; for instance, by allowing it to go to the aid of a friendly nation under attack, something it cannot now legally do. But Mr. Abe has also carefully insisted that he still wants to restrict Japan to a largely nonmilitary role

“No country is completely safe from terrorism,” Mr. Abe told Parliament last week. “How do we cut the influence of ISIL, and put a stop to extremism? Japan must play its part in achieving this.”

He has also emphasized that the $200 million in aid he offered two weeks ago was solely for humanitarian purposes. On Sunday, Mr. Abe proclaimed that he wanted to increase Japan’s nonlethal aid to countries opposing the Islamic State.

“The cruelty of the Islamic State has made Japan see a harsh new reality,” said Mr. Kubo of the University of Tokyo. “We now realize we face the same dangers as other countries do.”