Japanese scientists have estimated that nationwide potential of “Supercritical Geothermal Resources in Japan”, originating by the subduction of oceanic plates, reaches hundreds GWs. Power generation from the supercritical geothermal resources in Japan can contribute significantly to both energy security and reduction of emissions of CO 2 . The temperature range of the target supercritical rock body is about 400-500 o C and its depth is expected to be less than several kilometers. The depths of the supercritical rock bodies in Japan are much shallower those in other areas in the world, which brings advantages in terms of accessibility, economy, and safety. However, there are a lot of scientific unknowns about their nature, especially regarding rock-mechanical and geochemical behavior under supercritical conditions. Technological breakthroughs will be necessary, because the temperature and pressure conditions in the supercritical geothermal systems are far beyond the current technological limitations and also because experiences in previous ultra-high temperature geothermal drilling suggest that the presence of acidic geothermal fluid is likely. The Japanese government has recognized that supercritical geothermal power generation is one of the key technologies in its strategy to drastically reduce CO 2 emissions in and after 2050 (NESTI2050). In FY2017, funded by NEDO (New Energy and Industrial Technology Development Organization), a team of Japanese researchers from 14 organizations have started a national project to improve understanding of the nature of supercritical rock bodies and the engineering necessary to extract geothermal energy. This project is a feasibility study combining science, engineering, economics, and environmental issues.