https://blog.nicovideo.jp/niconews/230013.html
A few days ago on the 30th of October, DWANGO Co. has put new policies into effect for users accessing Niconico Douga and Niconico Seiga from overseas.
Videos with the following elements are no longer viewable from IP addresses outside the country.
- sexualization and abuse of children, and animals/characters resembling children.
- violence and suicide
- promotion of terrorism
- the manufacture of weapons and narcotics
etc.
While most of Nicovideo's video platform remains accessible, their art platform Niconico Seiga is now completely blocked for overseas users, including uploads that lack violence or child sexualization (source:*seiga.nicovideo.jp* rating:s)
If you're interested, I would suggest reaching artists you like to see if they can mirror their works elsewhere. VPNs can still access the full service as normal.