I don’t think the Japanese Navy has anything to fear from Russian naval forces. The Chinese however can overwhelm with numbers....
Russia has been making rapid naval improvements of their own, and are the 3rd largest navy in amount of ships behind China and the US.
It only makes common sense for the Japanese and South Koreans to develop their own independent nuclear deterrent. I would not take the risk of doing anything that could be construed as moving towards developing a nuclear arsenal if I were Taiwan though. That provocation would be immediately met by an invasion. The Pax Americana will be impossible to replicate. We won’t like the Chinese version.
Remember that Japanese land based aircraft is within striking distance to any of those ships.
I'd say the Japs have the advantage if shooting starts.
And, I'd also bet that the Japanese only have to put the parts together to have a nuke.