It's a bit unclear to me why you need an organization that advocates against nuclear weapons. I'd argue the “nuclear taboo” is just the product of.. I don't just seeing one nuclear test video? It doesn't take the cataloging of witness testimony to see it's terror (though that may be important in its own right)

I'm not intimately familiar with Japanese self-perceptions - but from the outside it seems like post-WW2 the country really leaned into a view that "nuclear weapons are terrible" to the point of distraction - instead of a more self-reflective "nationalism is terrible" or something along those lines. There seems to be much less anxiety about preventing getting into a similar situations that triggered WW2: neo-colonial military bullying and domination of neighbors, xenaphobic oppression of ethnic groups, sycophantic following of cultural leaders etc. and an intense worry about the more tangeable use of nuclear weapons - which I'd argue is something that even if it were to come to pass would almost certainly never involve the Japanese people.

I wonder how this seeming diversion of public attention is perceived in Japan itself.

As I understand it, the anti-nationalist narrative was repressed due to anti-communist agendas of the occupation forces (ex: freeing of nationalist war criminals)

Would be curious to hear from anyone Japanese on the topic