I feel fairly sure that Japan could sink 25% of the Chinese navy in a couple of hours! China wouldn’t have air cover and would be sitting ducks.
Interesting factoid of a changing world. The Japanese Navy is roughly twice the size of the Uk’s Royal Navy. 18 RN surface combatants -vs- 44 in the JMSDF. Three times the number of attack submarines (though the RN is nuclear)
And the British have one Helicopter carrier. The Japanese have 4. And the Japanese ships are ready for an STOVL, or VTOL jet.
Look at a photo of a Japanese “Helicopter Destroyer” and be ready for a surprise. And you can bet the thing is built with Toyota/Honda quality, and not some rebuilt Russian job.