UNKNOWN MORTAL ORCHESTRA No matter how sunny it was, he still insisted on dressing up like Nazgûl.

RUBAN NIELSON is just a couple days home from a long tour. He's a little dazed but not too out of it. He's got a month-long break ahead of him, the longest he can remember in a while, but his band is also playing its first hometown show since it released its splendid second album in February. Unknown Mortal Orchestra's II is a woozy, seemingly offhand affair, with Nielson's needle-sharp guitar-work and airy vocals leading a charge of very tight, very fucked-up funk.

While Nielson's an aficionado of classic '60s psychedelia and the kaleidoscopic world of sound those records perpetuate, he's more than ever drawn to the austere, solitary art of songwriting. "I just want the songs to be robust," he says, "so that they can just be played with guitar and voice and it will have everything you need. I don't want to rely too much on the recording or the groove or whatever to be the song. That's what I did a lot on this record. I got an acoustic guitar—because I'd never really played acoustic—just to find the skeleton of the song. It makes it more fun to record, because you can record it a bunch of different ways and it'll still be the song. As long as the song is good."

The terrific II definitely has its share of "good" songs, and even a couple masterpieces: A circling, almost classical guitar line and a melody that's both languid and full of urgency drives "Swim and Sleep (Like a Shark)." And "So Good at Being in Trouble" is a slow funk ballad that could have been cut from the cloth of Sly and the Family Stone's Fresh. Based on something a girl said to Nielson at a hotel room party, it's graceful, sad, sexy, and destined to be a future classic; expect starry-eyed wannabes to over-sing it on whatever the 2030 version of American Idol is.

"If I need a song I just write a song," Nielson says. "I never have writer's block or anything like that. I have a lot of sketches that don't get fleshed out, but if I don't think that the song's going to be one of the best songs I've ever written, then I usually just leave it. It's usually stillborn. But I keep all of that stuff, because sometimes it sounds better to me later on. 'Swim and Sleep' was something that I thought wasn't quite there, and then I came back to it and changed it around, changed the chords, changed the guitar part, and it ended up being something I'm really proud of now."

Nielson moved from New Zealand to Portland in 2007 with his band the Mint Chicks; that band, which Nielson formed with his brother Kody in 2001, had achieved massive success at home, but by 2010 it had disintegrated. "The Mint Chicks ended because I was not happy and was getting treated really badly. I was doing all the work, and I just felt like I was the one who cared the most about it and everybody was just kind of in it to pay their rent by that stage. I left because I just wanted to do something more creative, and the Mint Chicks were turning into this kind of weird, stagnant thing. We'd had such a good run that I didn't want to ruin the good things that we did. In New Zealand, the problem was this pressure: Either you continue to make creative albums that nobody gives a shit about, or you just go mainstream and sell out, basically, and make whatever everybody wants you to make. Both of those options just sounded stupid, so it was time to end it."

The first UMO tracks appeared anonymously online, gathering substantial buzz until Nielson went public. A record deal and tour followed, and now Unknown Mortal Orchestra has become a much bigger thing than Nielson ever intended. He's using the opportunity to dig deep into himself. "I really would like for there to be this group of albums so that if you listen to them, you just know me and you don't have to worry about anything else," he says. "It seems like a thing I have to do before I die—keep a diary of the way I was feeling through this whole time. Because I feel misunderstood a lot of the time. And it's also weird being in a different country."

Meanwhile, the group—rounded out by bassist Jacob Portrait and newly recruited drummer Riley Geare—is trying to stay sane on the road while selling out shows across the US. "It's just the classic thing of playing a show and getting really excited," says Nielson, "and then there's a bunch of people afterward who want to hang out and do stuff, and you just want to do that—because you know that you've got to be in the van tomorrow for six hours. It's just so tempting to stay out all night and get into trouble. Which is really fun, but after three weeks, stuff starts getting a little heavy.

"I know there must be people who can do this, so maybe it's an experience thing," he continues, "but I really can't do this whole rock 'n' roll thing and then go back and watch an episode of something on Netflix and go to sleep early. Three days of that and the shows start getting worse. These days I'm pretty much smashed out of my head when I go onstage every night. I'm drunk before I even get onstage. And I play better when I'm like that. People talk about sex and drugs like they're this perk that you can take or leave, but I kind of think it's a one-deal thing. I've seen people go on tour—we've been on a lot of support tours—and I've seen people that play the show, call their girlfriend, go home and watch Netflix, and eat healthy vegan food every day. After two weeks, they're crazy. And everybody that's doing a bunch of drugs and freaking out is actually kind of keeping an even keel. It's hard to be healthy on the road.

"When I'm home it's totally different," he adds. "I have a liquor cabinet at my house but I never even think about drinking, because I'm where I'm happy, just hanging out with my wife and my kids."

Nielson's pretty open in talking about the balance of rock stardom and domestic life, and it's a similar candor and honesty that makes Unknown Mortal Orchestra songs so compelling, even as they warp and stretch the sounds of pop and R&B with rubber-band elasticity. "I'm trying to be as revealing as I can be," he says. "I want to confess all my sins in my songs—for some reason I'm sort of obsessed with that at the moment—and then deal with the consequences."