The Japanese Maritime Self-Defense Force is quite capable of defeating the PLAN in a straight-up fight, without help from anyone else. Across the whole of their force, their level of technology is better and they're certainly better-trained. There's a high danger of a VERY embarrassing defeat for the Chinese in any conflict at any level.
Don't be fooled by the name; the MSDF is probably the second-most powerful navy in the world right now.
This. While the Japanese might lack the ability to project power across the globe like the British, French, and Russian navies, on a more local level, the Japanese Navy is an very powerful force.