Few forms of music have colonised the world like metal and hip-hop. Wherever you go you will find these two alchemising with local genres. A few years back, I took a trip to Kathmandu to visit a Nepali festival, where I saw bands from all over south Asia blasting through the beats, and in the streets outside the cabs threaded past with hip-hop blaring out of open windows. Both still represent youth in a way that lots of pop and rock no longer does. Hip-hop is simply the lingua franca of popular culture for anyone under 40; metal is still the most potent symbol of rebellion music has to offer – no matter that the rebellion is usually carefully packaged into a set of signifiers designed to tick adolescent boxes. But they are also omnipresent because both are malleable. They can be twisted into any shape, which means they do not sit still. Whereas a band playing Americana today will sound very much like an Americana band from 1980, the chances are that someone playing metal today will sound very little like a metal band from 1980.

Take A.A. Williams. She’s signed to Bella Union, the label founded by Simon Raymonde, once of beloved 1980s etherealists the Cocteau Twins, which specialises in woody sounding music of the kind often made by men with ragged beards and plaid shirts. But she also gets reviewed in Kerrang!and Metal Hammer. She makes heavy music that has indisputably come out of metal, but also exists somewhere between planes. There’s a good bit of post-rock in there, hints of the music that has become known as post-classical, and, in her pure, clean voice, bits of folk, even.

At a disappointingly undersold QEH, Williams and her band were breathtaking. It’s not that she was skipping between styles with dizzying ease – she played her forthcoming album As the Moon Restsin its entirety, then three encores – but that the cumulative power of it was both awesome and beautiful. One might note that pretty much everything across As the Moon Rests and its predecessor Forever Blue sounds more or less the same – the songs are long, mournfully paced, and all occupy a similar windswept, gothic sonic place (it’s a bit like someone reading Wuthering Heights to you through a megaphone). But Williams prefers melody to brute force (she has an astoundingly good voice, too), and understands the difference between using loudness to overwhelm and using it to overpower. Her songs never topple over into noise: they stay at the place where the waves crash over you without knocking you off your feet.

Her third album, when it arrives, will be the time when we discover whether there is more. One can create a career by running on the spot – just ask the Ramones, the greatest group in the history of recorded music – but Williams doesn’t seem the kind of person who wants to keep churning out the same thing to ever-decreasing returns.

There was more of a party atmosphere over in west London on Sunday night, where London’s Spanish speakers had turned out in force to greet Nathy Peluso, a young star of Latin hip-hop, over from Argentina (whose name makes me want to write Nancy Pelosi, every time). The young, largely female crowd cheered before she came on. They sang and rapped along to everything, and displayed their sexual fervour. Clearly, Peluso has a significant Sapphic following – bras were thrown on stage, and the knees of one half of the young lesbian couple standing in front me literally buckled when Peluso fellated the head of a rose before throwing it out to the crowd. It’s easier to pretend it’s not the case but pop music is meant to be sexy, and Peluso places sex front and centre in her songs (I confess that my understanding of hip-hop vernacular in Spanish is not what it once was, but looking up her lyrics in translation suggests a great many of them are about eating, and not in the sense of getting your five a day. Some are less subtle: ‘If I bend over, you can feel my clitoris,’ she apparently offers in ‘Sana Sana’).

She was a force of nature, coming on in black leotard, leggings and sunglasses, punching the air and high kicking through the dry ice like the Terminator recast as a member of Pan’s People. And she didn’t stop. An hour later, she managed a burst of one-armed press-ups like some bonkers bloke in the pub who really, really wants to prove himself. (‘Go on! Punch my stomach! Hard as you like! I won’t feel a thing!) It was easy to get carried away with the joyous energy of it all, but the live show slightly altered the balance from her albums, going a good bit heavier on the Latin than the hip-hop. Though still a minority taste in the UK, South American pop is exploding across the world, and perhaps Peluso’s current show is configured to make her seem more like an all-round entertainer than a hip-hop star. If so, that’s a shame, because it’s when she’s spitting out the words and the beats are hardest that Peluso seems most herself.