Japan needs nukes. I would nuke China with any aggression on their part.
No can do. Japan would be destroyed in a nuke counterstrike by China. Japan can assemble shelved parts into nukes within a few days time. They have enough weapons-grade plutonium for several hundred nukes. And probably a bunch of stockpiled parts ready to assemble. Nukes are a last resort by Japan. Their "self-defense" navy can pretty much destroy the Chinese navy without resorting to nukes.