Interesting! I did a quick search and found this (the links don't go to the websites) recent list.
https://www.similarweb.com/top-websites/japan/arts-and-entertainment/tv-movies-and-streaming/
Here is the top site below YouTube. It's pretty busy (https://www.nicovideo.jp/), but the rest are less so (https://tenki.jp/). Looking at the code (using F12) I think they are all basically content servers (like most commercial sites). I think the use of Kanji keeps the sites looking cleaner than English text would.