People are asking about Japanese law on this, so I'll write what I know. I am not a lawyer, just a person who cares about copyright.
Japan does not have fair use, instead it has a number of specific exceptions to copyright. For example, you can take photos of things semi-permanently installed in an outdoor area and use those photos for non-commercial purposes, even if you photographed a 2D artwork that might have copyright. You can read the copyright law in English here:
https://www.cric.or.jp/english/clj/cl2.html#art32
The most generous exception in the law (except maybe the search engine one) is for "quotation", Article 32. For quotation you must use only as much of the work as is necessary for commentary, clearly separate it from your own content, clearly attribute it, and the quoted content must be subordinate to your own content. Regarding the last point, that means you can't just say "this is a nice painting" and post the image, you have to provide some commentary on it. (No, that's not clearly defined, so you'd need to work it out in court if there was a dispute.)
In practice this doesn't matter much on social media, and things work out much like places where you have fair use, but sometimes people try to enforce all their rights. Usually the people they are upset at take down their posts, but I guess in this case that didn't happen.
One really unfortunate side effect of this is that Japanese Wikpedia has very few images compared to other Wikipedias. Things that would be fine in an article, like book covers, are excluded because their Wikimedia file page would not have commentary and, so the thinking goes, would be infringement. (I remember reading the discussion that came to this conclusion on a Wikipedia discussion page years ago, but haven't been able to find it since.) This is why the Japanese article for Anpanman has a photo of a mural, for example, while the English article has a book cover.
For moral rights (著作人格権), these actually also exist in many places besides the United States. Practically speaking, if you license a work for use it's pretty common to have a clause saying you will not exercise these rights, and if you're in a mutually beneficial relationship any concerns over how you're credited can usually be negotiated. In this particular case the use was completely unauthorized so that didn't happen. (I am still confused about why the poster didn't just remove the image when asked.)