Japan's push for the right to collective self-defence is posing a tricky question to regional powers: whether it is pursuing militarism that would threaten peace, or seeking its suitable security role that would contribute to regional and global stability.
Seoul and Beijing, two major victims of Japan's past imperialism, are wary of any possibility of its military recrudescence, while a financially strained Washington apparently welcomes Tokyo's desire to assume more security responsibilities.
Analysts say Seoul needs to make careful calculations for its long-term interests, particularly when the Sino-US competition over regional preponderance and Sino-Japan territorial spats intensify.
"Whether we oppose it or not, Japan will push for the right based on its strategic considerations," said Kim Heung-kyu, politics and diplomacy professor at Sungshin Women's University.
"While the right has yet to take shape, Seoul needs to carefully watch its developments, refrain from making emotional responses and explore ways to enhance our national strategic interests."
With official support from Washington, its key ally, Tokyo has sought collective self-defence ― the use of force to respond to an attack on its ally, namely the US ― by altering the interpretation of its war-renouncing constitution or rewriting it.
Japan cited increasing security threats from China and North Korea to justify its pursuit of the contentious right.
But its moves toward rearmament have unnerved South Korea and China, which have long been frustrated by its failure to fully atone for its wartime atrocities including forcing Asian women into sexual servitude during World War II.
Their long-simmering territorial rows have also deepened their distrust toward Japan's push for a "normal" state with a full-fledged military.
Mindful of the deteriorating public sentiment against Japan, Seoul has recently made clear that should Japan want to exercise the controversial right to defend its ally in a peninsular conflict, it must first secure Korea's consent.
Concerns here are that Japanese troops, which colonised Korea from 1910-45, would set foot on the peninsula again on the pretext of defending the US if its ally is attacked by North Korea.
But some experts point out that Seoul should also consider the practical security aspect that the US-Japanese alliance has been one critical pillar of peninsular defence along with South Korea's self-defence and the Seoul-Washington security alliance.
Japan hosts key strategic UN rear bases including Camp Zama near Tokyo, Kadena Air Base and Yokosuka Naval Base, which are to offer logistical support to US forces in case of an armed conflict on the peninsula.
The US and Japan are known to have in place "Operational Plan 5055," a war scenario under which Japan's Self-Defence Forces offer wartime assistance to US troops operating on the peninsula.
As Washington has supported Tokyo's desire for collective self-defence, observers raised hopes that the US might seek to keep Japan in check and lead it to contribute to regional peace within the constraints of the alliance ― as it did with regard to Germany within the collective security framework of the North Atlantic Treaty Organisation.
NATO's first Secretary-General Lord Ismay stated in 1949 that the organisation's goal was "to keep the Russians out, the Americans in and the Germans down."
With Germany registered as a NATO member, it has so far contributed to global peace and stability despite initial misgivings about the reemergence of the ill-fated war aggressor.
The US vision for Japan's expanded military role is expected to be unveiled next year as the two allies have agreed to revise the 1997 guidelines for bilateral security cooperation. The guidelines, first adopted in 1978 to counter Soviet threats, were last amended in 1997 to reflect post-Cold War security threats.
The revision of the guidelines is expected to dictate bilateral collaboration over China's increasing assertiveness, particularly over maritime territorial disputes in East and South China seas.
"How to evaluate Chinese threats would be crucial as their threat perceptions are not identical. How to compromise over it might be a major issue as they proceed with the revision," said Park Young-june, Japan expert at Korea National Defence University.
"The US appears to look at the deepening social, economic interdependence with China as well as the threat of its increasing military might. Yet, Japan appears to give more weight to China's military threat, particularly with regard to its territorial row over a set of islands in the East China Sea."
Security concerns about Japan have been heightened by Prime Minister Shinzo Abe, a security hawk who has pushed the limits of Article 9 of the constitution that bans Japan's right to wage war and possess potential war materials.
But experts say that Japan is unlikely to consider adopting a militaristic national strategy that once made it a defeated, pariah state.
"Under the framework of the US-Japan alliance, the revival of Japanese militarism is unlikely. First of all, the US doesn't want it as it is also one of the victims of the militarism," said Park of Korea National Defence University.
"Plus, South Korea and China are not the weak states, which Japan once encroached upon. There is little room for Japan to expand its power through militaristic approaches in the region at the moment."
But some analysts raise the possibility that an increasing military power coupled with surging nationalism could lead the former imperialist to reorient its national policy, particularly should the US ever lose its preeminence in the Asia-Pacific.
Under the so-called Yoshida doctrine, a postwar national strategy centering on economic growth based on security backing from the US, Japan had long refrained from military rearmament.
But as the international community has called for Japan's greater security contributions since the 1990s when the world struggled with ethnic, religious and other sociopolitical conflicts unleashed after the end of the Cold War, Tokyo has sought to explore a new national identity.
Washington has apparently wanted Tokyo to shoulder more security responsibilities commensurate with its economic scale, amid a host of domestic and global issues including financial woes, Iranian nuclear conundrum, Israel-Palestinian conflict and global terrorism.
But with nationalist, unapologetic right-wingers reviving the memories of its past militarism, Tokyo's moves toward rearmament have nonetheless been met with strong resistance from neighbouring states.
China's security concerns have recently increased as its deepening conflict over the chain of islands ― called Senkaku in Japan and Diaoyu in China ― has escalated.
"China feels very apprehensive about the move toward collective self-defence. But it takes a cautious stance as Beijing thinks a hasty or excessive response could give Tokyo a pretext to step up its pursuit of the right," said Kim of Sungshin Women's University.
"China also appears to believe that the US would not give inordinate autonomy to Japan as its excessive exercise of the right could undermine America's postwar order, and it could also be drawn into an unnecessary military conflict."