Extremely high temperatures are sometimes observed around Japan, not only during the day but also at night, resulting in considerable damage to crops, and health issues have been reported. While some research has examined such events in some regions, the overall picture is unclear. In this study, we focus on high-temperature events at night and report their seasonal and regional characteristics and future changes. The frequency of high-temperature events is investigated by using the non-hydrostatic regional climate model NHRCM with horizontal grid spacings of 2 km and 5 km. The target periods are 20 years, both in the past and the future. Nighttime high-temperature events, while less frequent than daytime events, occur across a wide area of Japan. The 20-year average frequency is less than two days per month, except in parts of Hokkaido, where it is over three days per month. The occurrence of high-temperature events varies by season and region. In Hokuriku region and the north-east region of Hokkaido, high-temperature events are most frequent in spring (March, April, and May), which is consistent with observations from previous studies. In other regions, these events occur most frequently in autumn or winter. And also in some regions, the frequency of these events shows seasonal variation with two peaks. The seasonal variation with two peaks in R02 is more distinct than that in R05. The analysis predicts that these high-temperature events will increase in the future across all regions, except for Hokkaido and parts of Tohoku.