Of the 66 states categorized as 'very high' in the 2020 Human Development Index 12 (including Japan) use the death penalty, another 5 have it on the books but are currently in moratorium, and another 2 réserve it only for crimes committed in times of war. That's 19/66, more than a 1/4 of the most developed states (and still nearly 1/5 if you exclude the moratorium and wartime-only states). Japan is far from alone.