Japan’s push for decarbonization is only half the story. The country also faces a structural vulnerability: it produces barely 13% of the energy it consumes, one of the lowest self-sufficiency ratios in the OECD. The global energy market disruptions in 2022 underscore how exposed Japan remains.

As policymakers sharpen their focus on energy security, a new cohort of startups is emerging with technologies aimed not just at cutting emissions but at expanding domestic production. And while some are in the realm of renewables, several top startups have set their sights on taming nuclear power: fission or fusion.

Supporting innovation in the nuclear field has been extremely tricky for Japan’s government ever since the 2011 Fukushima disaster. Even now, NEDO, the state R&D hub, is not allowed to channel any of the deep-tech funding to projects with nuclear affiliations. And while new PM Takaichi firmly supports the nuclear sector, public sentiment remains ambivalent. A recent survey by JAERO, the atomic sector’s advocacy group, showed 58% of respondents view nuclear somewhat positively, yet more than half say the word “danger” is the first association that comes to mind.

For now, the safe space for nuclear funding – both public and private – seems to be in fusion. Last year, the government set up the Japan Fusion Energy Council (J-Fusion), and in the first half of FY2025, startups in the fusion sector raised ¥5.9 billion, according to Speeda’s Japan Startup Finance.

The most prominent of the fusion startups is probably Kyoto Fusioneering, partly thanks to winning supply contracts to the U.S. national fusion facilities. But there are other fusion and renewables startups in Japan worth noting. We review several below, as well as key sector trends.