Fossil-fueled thermal power generation accounted for 71.7% of total electricity generated during the year [2021], down from 74.9% the previous year [2020]. Coal and LNG accounted for 26.5% and 31.7%, respectively, and both fossil fuels are on a declining trend. Nuclear power accounted for 5.9%, up from 4.3% the previous year.
Source: https://www.isep.or.jp/en/1243/
Reference #4