If I thought moving before the World Court would do any good I'd advocate for that. But. Lately, the Philippines was only successful with a complaint against China because China never answered the complaint. China is taking a military profile to be power to contend with that no court order is going to matter.
I think the only way Japan can protest it's sovereign rights is to develop their military and take the circumstances before the UN Security Council. China is a permanent member of the council and would veto any resolution requested by Japan. Even with a vetoed resolution Japan will be on the record.
...Tokyo is becoming increasingly concerned (click here) that Beijing could use undersea exploration to extend its reach into Japanese waters, weakening the median line as the defining maritime barrier.
Japan's powerful coast guard retains the upper hand in the East China Sea, for now. But China is quickly closing the gap, and it may not be long before Beijing's naval forces outstrip Tokyo's. Moreover, it was recently disclosed that one of China's platforms is equipped with a military-grade surface radar system, improving China's awareness of activity in the East China Sea. This poses a serious problem for Tokyo: As development of the eastern side of the median line continues to lag, and as Beijing's maritime capabilities improve, Japan may have a harder time stopping China from pushing its territorial bounds eastward.