"The purpose of Japan's response is to send a message that we will be ready and we will resist if there's an invasion (of Japanese territory), that we will not allow the borders to be changed by force," said Iwama.

"We don't want a real war, the objective is political -- that China is persuaded from an aggressive act like the one that Putin has taken in the last several days and weeks."

It's against that backdrop that Japan's former prime minister, Shinzo Abe, raised a previously unthinkable suggestion during an interview three days after the Russian invasion.

Abe, still an influential figure in the ruling Liberal Democratic Party, floated the idea of Japan entering a NATO-like nuclear weapons sharing program -- hosting US nuclear weapons on Japanese soil. It was a shocking proposal for country that suffered the devastating impact of the two atomic bombs dropped on Hiroshima and Nagasaki during World War II -- but one Abe says should no longer be taboo.

Different times, changing tactics

Japan's response to Russia's invasion of Ukraine differs markedly to its actions after Moscow's attack on Crimea in 2014.

Then, under Abe, Japan was called out for being too slow to act. Now its strategy is different -- and the urgency arguably greater.

Back in 2014, Abe adopted the tactic of pulling Russia closer to prevent it tightening ties with China, said James Brown, an associate professor of political science at Temple University in Tokyo.

Russia had annexed the Ukrainian peninsula of Crimea by sending in armed forces to take over key facilities and foment a separatist rebellion that rumbled on for eight years.

Tokyo initially treated Russia's annexation of Ukraine's Crimea region as a Western issue, according to Sheila Smith, a senior fellow for Asia-Pacific studies at the Council on Foreign Relations.

"(The Japanese government) treated it a little bit like an issue for the Europeans and Americans to deal with; that it wasn't really about Japan, but that they'd go along with it," Smith said.

She said Abe harbored hopes that Russian leader Vladimir Putin would sign on to the normalization of Russia-Japan ties or a full peace treaty formally ending hostilities dating back to World War II.

However, this year the scale and horror of the crisis unfolding in Ukraine has prompted Japan to push a consistent message of unity with its G7 partners to show it's a "trustworthy partner," according to Brown, from Temple University.

"You hear time and time again, the government say -- 'and alongside our G7 and other international partners, we will coordinate in taking a tough response on this issue' -- they don't want to be seen as out of step," Brown said.

Japan needs G7 support -- particularly from the US -- to contain any move from Beijing on Taiwan, the island which China claims as its territory despite having never governed it.

Experts says Japan wants to keep in step with its international allies in the face of the unfolding human tragedy and China's growing military might.

'Sense of urgency'

China is considered a major threat, but the combined strength of Russia and China has put Japan under considerable pressure.

Foreign vessels are permitted to sail through the Osumi and Tsugaru straits -- both international waters -- but Japan closely monitored the maneuvers, which the country's Defense Department called "unusual."

Japan's Ministry of Defense said on Friday that 10 Russian Navy vessels, including a frigate, had sailed through the Tsugaru Strait the previous day, toward the Sea of ​​Japan.

And then there's Taiwan, which sits to the south in waters used to ferry 90% of Japan oil supplies.

Some say the Ukraine crisis on top of local security considerations shows it needs to commit even more.

Breaking down taboos

But extra defense funding is just one aspect of Japan's armor against an escalation of regional tensions.

Last month, Abe has used his position as former leader to raise another even more controversial prospect -- the idea of hosting US nuclear weapons in Japan.

"Japan is a signatory to the Nuclear Non-Proliferation Treaty and has its three non-nuclear principles, but it's essential to understand how the world's security is maintained, and we shouldn't treat those discussions as a taboo," Abe told Fuji Television.

Kishida immediately dismissed the suggestion, calling it "unacceptable," while anti-nuclear activists were predictably outraged.

Japan falls within the US nuclear umbrella but has long ruled out hosting nuclear weapons due to devastation wrought by atomic bombs dropped during World War II.

When asked about Abe's comments in a regular press briefing, China's Foreign Ministry spokesman Wang Wenbin said Japanese politicians had made "wild comments" that "openly violate its own Three Non-Nuclear Principles and the obligations of a party to the Nuclear Non-proliferation Treaty (NPT)."

"By raising nuclear sharing with the US, Japan has fully exposed the dangerous tendency of lingering militarism in the country," he added.

In the interview, Abe also called for the US to take a more explicit position on the defense of Taiwan over whether or not it would defend the self-ruled island if Beijing were to attack.

However, later a government official said the US was not announcing any change to its policy on Taiwan -- under the "One China" Policy, the US acknowledges China's claim of sovereignty over Taiwan.

One thing is clear: Russia's attack on Ukraine has rattled the Japanese and has forced them to face questions some might otherwise avoid.

"People are asking, 'Will the United States really come in if the Chinese attack? Will the United States go to war with China?'" said Smith, from the Council on Foreign Relations.

"These are all recent questions that have been bubbling up under the surface, based on the capabilities first of North Korea, but also China. And I think that's also being laid bare as Putin uses nuclear threats," she added.