I saw an obscure film called Village of Doom 1983.
It's about the Tsuyama massacre where a young man with TB murdered almost his entire village over the course of a single night. He was ostracized by succubi for having TB.https://en.wikipedia.org/wiki/Tsuyama_massacre
It's a great film. I like how it takes a very neutral view of the protagonist. It doesn't artificially portray him as a scumbag as he transforms from a nice guy into someone who just snaps.
The last 30 minutes are great. It's frantic and unrelenting as he runs through the town murdering everyone with his shotgun and katana with sadistic glee. There's a lot of first person camera shots too.
Unfortunately the only place I was able to find it was avistaz. It's a great tracker and I got into it pretty easily recently by hanging around on their invite discord server until they randomly did a sign up one day. I love old japanese films so it was well worth it for me. I highly recommend it for anyone interested.