Reacting is Natural

Those who like to minimize China's growing military capabilities like to say it is natural for a China getting richer and with distant sources of raw materials to want greater naval and air power to protect those imports. This is true, but it doesn't erase the reality that those capabilities can be used for anything that the Chinese rulers decide is a goal.

As China's naval and air power increases, Japan naturally gets nervous as Japan's sea lines of communication that run past China become vulnerable to that increased Chinese military capability.

Japan reacts by trying to build up their own capabilities facing China.

And helping the Philippines hold their strategic position on Japan's line of communication becomes important:

The Nihon Keizai Shimbun [newspaper] reported on Thursday that Japan has decided to provide the Philippines with patrol ships, to support the island country in its territorial dispute against China.

You'll recall that Japan invaded the Philippines in 1941 to prevent this American colony from threatening Japanese supply lines. Geography doesn't change.