>>149556125As this anon said
>>149559341, it presumably can vary significantly depending on the region and on the endemic demographic proportions of ancestral Yayoi and Jomon admixture.
The Jomon people (despite what /pol/tard memes and shitposting might lead someone to believe) were genetically closer to Austronesians than to Caucasians, and generally had darker complexions than the Yayoi, an ethnic group related to the ancient Koreans.
To cut to the chase, the rs1800414 G allele of the OCA2 gene, which is associated with lighter pigmentation among East Asians, is actually quite widespread in Japan, having a frequency of 79%.
Of course, that percentage also means that more than a fifth of the Japanese population is likely to have noticeably darker skin tones.