China has been warned to stay alert to the possibility Japan will intervene militarily in the event of an attack on Taiwan.
A research paper said recent gestures of support for the island indicate that Japan and the United States have been discussing the scenario and are making plans to deter Beijing from using force to take the island.
"Japan has not only released signals through official and individual levels, but also tried to carry out practical response actions through the Japan-US alliance or partially acted alone under the existing legal framework," said the paper published last week in the journal Asia-Pacific Security and Maritime Affairs.
Although the Japanese constitution renounces the right to wage war, and the public may be reluctant to get involved in a conflict, the paper said there were at least three scenarios where a 2015 national security law authorized the Japanese Self Defense Forces to get involved - either by providing logistical support to the US, invoking a "collective defense" clause to join the US in defending the island or US bases in Japan coming under attack.
Beijing regards Taiwan as a breakaway province and has never renounced the use of force to reunite it with the mainland, but Japan would regard this as a significant threat to its national security and the regional political order.
The paper, written by Wu Huaizhong, a researcher with the Chinese Academy of Social Sciences, said that in recent years the Japanese government had hardened its stance.
"It is hard to imagine that in the short and mid-term future Japan will actively seek to be involved in an uncontrollable disastrous war regardless of the cost," the article said, adding that it is more likely to consider providing logistical support to allies rather than becoming directly involved in combat.
"The question is not 'whether' Japan would intervene, but just 'how' to intervene," it added.
The Japanese and US navies have conducted a series of joint drills in recent years and last week saw their first joint anti-submarine drill in the South China Sea, a move seen as targeting China.
Meanwhile, other Chinese researchers have warned that Japan may try to use United Nations peacekeeping missions to become a major power.
"(China) must watch their attempts to use such opportunities to circumvent the Peace Constitution," an article on the website of Tsinghua University's World Peace Forum by researchers Hu Fangxin and Zhang Lihua warned.
Japan only started dispatching its armed forces to take part in UN missions abroad in 1992, and since restrictions on its mandates, access to weapons and peacekeeping activities have been gradually loosened.
The paper said these operations have increased public support for overseas action, improved the country's ability to project military power and enhanced its diplomatic autonomy.
It said the 2015 national security law had given the Japanese Self Defense Forces the right to join "collective defense" operations and significantly expanded their mandate.
"The Japanese government has broken through the 'exclusively defensive' restrictions ... forcing through the process of constitutional revision with a fait accompli," it said.
Liu Jiangyong, a specialist in China-Japan relations at Tsinghua University in Beijing, compared their core relationship to a chess game.
"On the issues such as history, Taiwan, the Diaoyu Islands (which both sides claim and are also known as the Senkakus), maritime rights, regional security, Japan-US joint defense, and most recently Xinjiang and Hong Kong, there are sharp conflicts and oppositions," he said.
Liu argued that China was concerned that Japan had ambitions to become a global power, while Tokyo wanted to contain its neighbor.
He compared their respective strategies to a game of Go in which Tokyo was teaming up with the US, Australia, India, Nato and Association of Southeast Asian Nations to check China, while Beijing was counting on the Belt and Road Initiative, its transcontinental infrastructure project.
Zhang Jifeng, a Japanese studies specialist from the Chinese Academy of Social Sciences, said: "When (the Japanese Self Defence Forces) are having a drill in South China Sea, it would obviously be against the Peace Constitution."
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