If you’ve never been to a Brotherhood show, or been within a 5-mile radius of one, you might be excused for thinking the local metallurgists are some kind of hippy-dippy peace-and-love outfit — an acoustic Christian-rock act, maybe, or a reggae band made up of trust-fund babies with dreadlocked blond hair. But think “brotherhood” not in the sense of a saccharine plea for global unity but rather an organization of sinister, hooded monks performing ritualistic human sacrifices for some shadowy purpose. A quick listen to “Waiting for Mashiach” — which directly pits an exultant “whoa” chorus against former bull rider Rod Nichols’s brutal growls, suggesting maybe the antichrist showed up instead — should clear up any confusion. Brotherhood is a hard-hitting standout in a city full of high-caliber shredders and screamers, and Friday marks their last SA appearance before they cut a swath of unimaginable horror from the Midwest to the Deep South — otherwise known as “touring.” They won’t be back until September, and by then they may have already collected the final stone of Malphas and entered the seventh chamber of Gehenna `citation needed`. After that, all bets are off.