I believe in this particular case it's Bm-Em/B-Bm-Bm7-Bsus2-Bsus4 with a B note layered an octave higher.

That last one is quite interesting because it's two fifth intervals in one chord (B-F# and E-B), but differently than a m7 or M7. I think it's there to resolve both the sus2 and the m7 at once, but in two different ways.

I agree. I think the fifths are a power interval/tension enhancement allowing the tension to disappear at resolution like a magic trick.

Are you certain it's an ordinary B minor chord to start out? I cannot help but hear a unique quality. Right at 4:14, under the B, the harmony feels like an A just a major second down, yet it's not an A. I've been listening to intervals like the septimal minor third and nothing sounds quite like it so far. Maybe it's just the timbre of their voices or something

Well, they do these weird inflections that might throw it off, but disregarding those it should be just a Bm.

That last one is quite interesting because it's two fifth intervals in one chord (B-F# and E-B), but differently than a m7 or M7. I think it's there to resolve both the sus2 and the m7 at once, but in two different ways.

What type of harmony/interval is playing at 4:14-4:26 in this song?

I've also heard this interval in the Ar Tonelico ost, Ghost in the Shell soundtrack, and maybe Panzer Dragoon Orta... it sounds very cool so I want to replicate this sound.

EDIT: I hear it's related to "Bulgarian polyphony" ... are there any resources online for studying that?