Spike Japan is another well-written blog covering poverty & decay in Japan, specifically Tokyo. It also has nice photos of things rusting. https://spikejapan.wordpress.com/
I've never really looked at this before. It seems to combine an interesting topic and a fair bit of research with, frankly, writing that is a little bit obnoxious. But still worth looking at.
Sorry, it actually covers Hokkaido.
Poking around it seems like the older posts are about the Tokyo area and the newer ones about Hokkaido.