Japanese metalcore/screamo/(emo) rap. Clean vocals start around 18 seconds in.
If that's too heavy for you, how about some post-rock?
I think these should sound cool even if you don't understand the lyrics. Out of left (or right?) field compared to most of the stuff posted so far, but hopefully you find these interesting if nothing else.
If you like the first vocalist, good news! There is
a lot more of her (めらみぽっぷ / Meramipop)
https://www.youtube.com/playlist?lis...cjPB0FfpPdNKDF
If I had to pick one song to showcase her incredible treble: (symphonic rock)
Doesn't sound great on youtube, but you can find my CD rip from my Twitter (@Merami_fan).