I can tell I've been listening to this Japan Suicide album for a while because of two reasons: for one thing, I've found myself singing along with these songs, which is not something that would come easy because this isn't really pop. But another thing is that my notes still say that this has a sound where I would enjoy seeing them perform live on New Year's Eve, so I've obviously been listening to this since late last year.
The sounds of Japan Suicide could be placed into a number of different genres, but what it is important is not what those individual genres are but what happens when they all combine at their various levels. There is a psychedelic quality to these songs and I think it's because the fuzzy distortion seems to paint this cloud around the music-- I imagine them performing live in a cloud of fog for some reason.
At the same time, there are pieces of a band like The Cure in here but in a more modern take as well. I'd assume that goes into something sort of -gaze category, perhaps shoegaze but perhaps a subgenre of it as well. Maybe dreamgaze, psychgaze or darkgaze (or all three?) depending upon if those are real or not and what they mean.
In addition to that there is a metal feel to this. Sometimes it can remind me of A Perfect CIrcle and other times it can remind me of Far. It's not something where if you don't like metal though ("That music is too loud for me!") you'll be turned off by this because that seems to be one of the smaller influences in these songs.
What you have to realize- the amazing part of "Santa Sangre"- is that these different genres don't change from song to song. It's like "Oh yeah, this is their heavy song and then this one is their really trippy song". These elements are blended together and come out in all of their songs.