TOKYO • At first glance, this week's visit to Japan by Indian Prime Minister Narendra Modi seems unexceptional - it's the third annual summit between Mr Modi and Japanese Prime Minister Shinzo Abe, the sort of regular geopolitical dating event undertaken by world leaders and usually resulting in just a joint communique that is forgotten just as fast as it is written.

But this time it is different, for when Mr Modi's plane lands in Tokyo on Thursday, he and Mr Abe could well be making history by putting the finishing touches to an India-Japan alliance that has the potential to change the balance of power throughout Asia.

It is an alliance which Japan has conceived and assiduously promoted for more than a decade. And it is one that has the potential to alter profoundly the military power projection capabilities of both nations.

Japanese politicians and officials have long ago drawn the conclusion that their country is engaged in an existential confrontation with China. The confrontation may not come to actual blows, and economic cooperation may continue to coexist in parallel to strategic competition. Still, a rising China not only appears destined to marginalise Japan as an Asian power, but is also determined to challenge Japan's territorial possessions, as the current spat over the Senkaku/Diaoyu Islands indicates.

And, since the disparity between the two nations' sizes and resource potential is so big as to be essentially unbridgeable, Japan's only hope of escaping from its China predicament is through forging a new system of regional alliances. Yet that is easier said than done, for although many Asian countries share Japan's concerns, not many share Japan's historic baggage or singular obsession with the Chinese threat.

To make matters more complicated, any regional alliance that Japan forges has to be compatible with - or at least not contradictory to - Tokyo's all-important security relationship with the United States. Mr Abe's courtship of Russia has largely failed because it did not pass that hurdle, coming at a time when US-Russia relations are nosediving.

WHY INDIA IS PERFECT FIT FOR JAPAN

Seen from this perspective, India remains Japan's perfect fit for at least three key reasons. It is big enough to provide a counter-balance to China, an objective which not only New Delhi and Tokyo but also Washington share. The Indian economy is also large enough to provide an alternative manufacturing base for Japanese industry, thereby allowing a diversification away from China, an argument that is music to the ears of Mr Modi, who as former chief minister of Gujarat is familiar with the Japanese-designed Delhi-Mumbai Industrial Corridor, which will act as a logistics base for hundreds of Japanese firms. And just as importantly, a link with India, a big Asian democracy, confers on Japan added regional legitimacy of a kind its alliance with, say, Australia, cannot provide.

The architects of Japan's strategic tilt to India are its Deputy Chief Cabinet Secretary Nobukatsu Kanehara and Mr Tomohiko Taniguchi, Mr Abe's special Cabinet adviser. As anyone who has met them would readily attest, they are among Japan's most influential and original thinkers. And their efforts date back to the first stint of the Abe leadership, when they authored the Japanese Prime Minister's August 2007 speech to the Indian Parliament, which evoked a grand vision of a "confluence of the two seas", a "strategic global partnership" dedicated to nurturing an "open and transparent" maritime zone which links the Pacific and Indian oceans as part of "a broader Asia".

The usual vagaries of Japanese politics subsequently intervened: Mr Abe resigned for health reasons just a few weeks after delivering this seminal Delhi speech, and the successor Japanese government showed no interest in the idea. But it is testimony to how serious the matter is being viewed by Mr Abe that one of the first initiatives he undertook upon returning to office in December 2012 was to relaunch his courtship of India under a plan to create what he termed "Asia's Democratic Security Diamond".

This was to be a grand partnership based on a determination to prevent the South China Sea from becoming "Beijing's lake" and a realisation that, as Mr Abe put it, "peace, stability and freedom of navigation in the Pacific Ocean are inseparable from peace, stability and freedom of navigation in the Indian Ocean".

Yet this proved to be a misstep: Mr Abe's "security diamond" concept was initially rejected by India as having too many rough edges, as being too provocative to China, and even Japanese diplomats admitted that their Prime Minister may have been too strident in his appeals. Still, Mr Abe's dogged determination is not easily deflected and it bore fruit when Mr Modi became India's prime minister in June 2014.

During Mr Modi's visit to Japan in September 2014, Mr Abe had already secured an agreement to upgrade the Japan-India relationship to a "special strategic and global partnership". And Mr Abe's visit to India at the end of last year built substantially on this achievement by including an agreement on weapons and defence technology development.

The Japanese have also showered India with economic cooperation projects, including a plan to finance and build India's first "bullet train" and the elaboration of a memorandum of understanding on nuclear energy, something which Mr Modi is keen to have, since it will facilitate American nuclear energy vendors in sourcing Japanese equipment for supply to India.

Both sides know that a huge gap remains between words and deeds. Indian bureaucratic red tape has restricted Japanese investments. The first Japanese-built train, connecting Mumbai with Ahmedabad, will not be ready until the middle of the next decade at the earliest.

Meanwhile, Japan's offer to sell its US-2 amphibious search and rescue aircraft to India - at effectively below production costs - is stuck. And reaching a nuclear power deal with India, a country that is not a party to the Nuclear Non-Proliferation Treaty, is not an easy option for Japan.

But the biggest problem for Japan is that India continues to see itself as essentially a land power with complicated land borders that need defending. So, although the Indians are worried by the Chinese navy's increased presence in the Indian Ocean and Chinese plans to build a base in Gwadar Port in Pakistan, not all strategic planners in Delhi are convinced that India's best response to this Chinese naval challenge is a substantial Indian naval presence in the South China Sea, or even farther eastward beyond that, as Japan hopes.

Still, from his book-filled office in the Kantei, the Japanese Premier's official residence, Mr Kanehara, the Deputy Chief Cabinet Secretary, remains as resourceful as ever in boosting his country's links to India. Japan's latest and most spectacular gambit is to persuade India that Japan's military could assist the Indians in maintaining their supremacy in the Indian Ocean.

Japan has just announced that it will lease additional land early next year to expand a military base in the East African country of Djibouti, as a counterweight to what it sees as growing Chinese influence in the Horn of Africa and the Indian Ocean. In addition, Mr Abe is planning to offer assistance to Indian-Vietnamese offshore oil and gas exploration efforts in the South China Sea.

And Tokyo is also weighing proposals for joint Indian-Japanese infrastructure investment projects in Sri Lanka, another place where the Chinese navy has sought a presence.

Each one of these efforts is designed to persuade the Indians that Japan is prepared to contribute to their security, in return for an Indian partnership in the protection of Pacific strategic stability.

Japanese security planners readily acknowledge that even if Mr Modi's visit later this week goes smoothly and even if all the projects between the two countries bear fruit, it will be years before one could talk about a formal military alliance between the two nations. Nor is anyone in doubt that nothing will be able to supplant the importance of the US naval presence.

Still, India and Japan are steadily expanding their power projection capabilities. Both are now taking greater strides as global powers.

And both assume that the challenge from China will continue to provide them with plenty of opportunities for drawing even closer together.