Launched in August 2020, Cultural Japan. More than a million items on Japanese Culture, in a user-friendly interface.
On searching it becomes apparently that it’s an aggregator. A search for cat for instance, brings in results by Japanese artists and photographers from all over the Anglosphere and Europe, whereas one might have expected it to draw on Japanese digitised collections. Only one result came from Japan, from the University of Tokyo General Library. However, it appears this is simply an artefact of my search. If I search for cat using the Japanese Kanji 猫, then the search results are indeed a mix.
It seems no large versions of pictures are on-site, and the searcher must follow an off-site link and hope for the best, negotiating various links and viewer types to try to get a large version.
In the case of a test picture, “Scouts near Niu-chang on a snowy night”, after about four pass-throughs the largest version at the final landing site was 800px. However, a quick Google Search for the same picture’s title “as a phrase” found a large version via Google Arts & Culture. This was not picked up by Cultural Japan. This is worth remembering if you get to the end of the click-chain and still only have a small picture.