Japan's toy is not only beautiful but very delicate and deadly...
It is certainly a nightmare for chinese.
IF you know anything of current naval power, you wouldn't make that statement.
First, all Japanese combat vessels uses old radars that have since been passed by Chinese radars on the 52D and C. As well, as several European powers and the US.
Second, most Japanese vessels are based more or less on the American Aegis, but then again so is the Chinese one.
So thank the Americans for that design.
Third, Japanese ships by design and constitution are defensive ships, meaning anti ship, anti air, anti missile, but no ground attack capabilities and even its AEGIS systems are stripped, as well as its fighters by the Americans to need American ships by it's side for it to work effectively or at all in an offensive capacity.
Fourth and most importantly, American strategy on the seas require all AMERICAN resources, most of which the Japanese doesn't have. In other words, Japan can't even fight properly without the US, even if all its systems are not stripped, which it is.
EX would be drones, satellite(Military version), missiles, nuclear subs, air power, and more.....
Having said that, the Japanese navy is quite strong, in an all out battle, we would still win, but with heavy loses. What we are doing now is to reduce loses, with each passing year, we are reducing loses on our side and increasing it on theirs.
Japan will not come to Vietnam's aid, they know they will take heavy casualties win or lose, and would Japan do it for Vietnam? If you follow Japan, you know despite all the sabre rattles, Abe cares about his economy first and foremost. To put it bluntly, he would defend China before he attack it. Japan needs economy not a victory.