Jesse Johnson. August 17, 2016. Cold War relic or necessary evil? U.S. ‘no first use’ nuclear proposal stirs divisions in Asia. The Japan Times, http://www.japantimes.co.jp/news/2016/08/17/national/cold-war-relic-necessary-evil-u-s-no-first-use-nuclear-proposal-stirs-divisions-asia/#.V7Rx9aKYK5oThe article states that building a nuclear stockpile in Japan is largely unthinkable:
Tokyo has expressed concerns over any move by the U.S. to adopt such a policy, reportedly calling it “unacceptable” from a Japanese security standpoint.
Still, building a nuclear stockpile — even with a belligerent neighbor like North Korea — is unlikely to gain traction in Japan, the only nation to have been attacked with atomic weapons.This assertion that Japan is unlikely to build a nuclear stockpile is inconsistent with allegations that Japan has a "bomb in the basement":
Robert Windrem. 2014.Japan Has Nuclear 'Bomb in the Basement,' and China Isn't Happy. NBC News, http://www.nbcnews.com/storyline/fukushima-anniversary/japan-has-nuclear-bomb-basement-china-isnt-happy-n48976The tangled webs we humans weave...
...government officials and proliferation experts say Japan is happy to let neighbors like China and North Korea believe it is part of the nuclear club, because it has a “bomb in the basement” -– the material and the means to produce nuclear weapons within six months, according to some estimates. And with tensions rising in the region, China’s belief in the “bomb in the basement” is strong enough that it has demanded Japan get rid of its massive stockpile of plutonium and drop plans to open a new breeder reactor this fall.