We have analyzed scenarios of Japanese energy systems in the 21st century with special focus on the electrification and climate change mitigation. We have described the causality pathway as to how the major drivers will have impacts on the structure of energy systems and found the followings: (1) Steady electrification in the building sector is expected driven by technological progresses and social change in the absence of climate change policy; (2) With strong greenhouse gas emission constraints, the combination of accelerated electrification across all sectors and de-carbonization of power generation is most likely to evolve in the future. The scenario analysis demonstrates the unique and important contribution of the Japanese innovation cluster for the global efforts to mitigate climate change through the development of energy technologies.