If I’m not mistaken, the idea I believe was that if they settled on and developed hydrogen infrastructure, that would power not just cars, but also heavy machinery, etc that other parts of the Honda/Toyota/Mitsubishi/etc conglomerates could use.
Politicians like hydrogen because if you ignore all the crap to get their (drilling for fossil fuels, separation, energy use in compression, transport, capital costs of building networks etc) you get that picture of water out of a tailpipe. The physics of it remain very poor.
As a point of ref we have relatively clean electricity generation already (hydro, solar, wind, nuclear) depending on what you count.
Any indication how close to production this east china sea resource is? How willing China is to let Japan develop it or is it already well developed? Again - these are often pipe dream type ideas.
I think it has more to do with external independence/isolationism, than about environments theme, carrying over from the century before. I don’t understand why the government just go double down on nuclear fuel cycle concept but maybe there are too much political complications in it.