Almost all Japanese editions of albums by foreign artists contain Japan-only bonus tracks, but few of these tracks are as site-specific as the one that closes the debut album by the New York-based postrock quartet Battles.

The title, “Katoman,” refers to a Tokyo concert promoter who goes by that nickname. Working alone, he has become something of an underground legend, and may have affected music on an international scale more than he realizes.

“The first tour we did here in 2004 was 11 shows,” recalls Battles’ Ian Williams, sitting in the noisy press hospitality area of Naeba Prince Hotel at the Fuji Rock Festival, where his band will take to the White Stage later in the afternoon. For lunch, he is eating individually wrapped chocolates and drinking mineral water.

“We didn’t even have a record out at the time. We were a brand new band. Why does anyone even know who Battles is, and why would they want us to tour Japan?” says Williams. “But Katoman called us and was like, ‘Oh yeah, I’ll bring you.’ ” Williams says the tour gave the band a chance to try themselves out.

“It was the first time we played a number of shows in a row, which is good practice. And the Japanese crowds were enthusiastic, which was encouraging because in New York we’d all been in bands and our friends were critical: ‘What are you guys trying to do?’ ” he says. “In Japan it was the first time I thought, ‘This band can be really good.’ ”

It would be 3 years before the group released their debut album, which is hardly a lifetime; but in these days of the instant bedroom-recorded CD, Battles’ gradual development is worth pondering, especially since that debut, “Mirrored,” released last spring, is not only one of the most acclaimed albums of the year, but a hit; or, at least, a hit by postrock instrumental standards.

Williams says Battles came together “in slow motion,” and that the core was his own tentative solo project. Previously, he was the guitarist in the instrumental rock group Don Caballero, who broke up in 2000. “I realized I still wanted to play music live,” he says, “so I started doing improv guitar shows by myself, and though I enjoyed it, I don’t think I was stimulated enough.”

He met experimental composer Tyondai Braxton, son of avant-garde jazz musician Anthony Braxton. Tyondai uses effects pedals and loops to alter his voice into various instrumental melody lines, from which he builds compositions in real time.

“He encouraged what I was doing,” Williams says, “but I wanted to do something more, so I said, ‘Why don’t you help me?’ ”

Williams knew guitarist David Konopka from the band Lynx and asked him to help out. Realizing he was forming a band, he went ahead and asked drummer John Stanier of Helmet to join — “It was no longer a solo thing.”

Still, the quartet didn’t really know what to do with themselves. The only thing Williams knew was that he didn’t want to play the same music he had played with Don Caballero or his other band, Storm and Stress, both of which marched under the postrock banner, meaning their music was challenging without necessarily abandoning the conventions of rock. By the time he quit, the music had “become a dead end,” he says, a comment that takes on special meaning as the other members of Don Cabellero have reunited without him.

Working with Braxton, Williams wanted to explore some of the electronic music directions he had taken as a matter of necessity at the end of his stint with Don Caballero.

“In 1998, I started using a loop pedal because our other guitarist quit. I could put a riff down and play off of it,” he says. “I was doing that and Ty was doing his loop stuff, and that inevitably gave the music an electronic character.”

Williams also wanted to add keyboards to Battles, but his initial idea was perhaps a little too high-concept.

“It was an organ, a drummer and 12 screaming female Iggy Pops, which is a quixotic notion, because how do you find those people?” But try they did, to the point where they placed ads and held auditions. “The only good person we got was a Japanese girl from Tokyo. She had guts. She’d do, like, splits in the air and scream at the same time.”

The band quickly abandoned this tack, but Williams says the misadventure had a silver lining.

“It disoriented me from any previous agenda, and we finally started focusing on music.”

Battles soon recorded two EPs that were experimental in the sense that they sounded like the products of a band consciously trying for something different. But they still rocked, thus attracting the attention of people who were looking for a blend of headbanging and electronica whimsy that didn’t sound arch or academic. One of them was Scott Herren, the hip-hop producer who usually works under the name Prefuse 73. He not only invited the band to open for him on tour, but got them signed to England’s Warp Records, which suddenly gave them worldwide distribution. Warp repackaged the EPs as one CD.

Familiarity with the EPs could not prepare one for “Mirrored.” For one thing, Braxton found a way to incorporate his instrumental vocal creations in an organic and witty way.

“Also, Dave started playing bass,” says Williams. “At first he was playing guitar, but it was just stuff left over from the other bands he played in.”

The crystallization of Battles’ sound was “Atlas,” the first single from “Mirrored” and one of the most startling rock songs of the year: big, brash, rhythmically irresistible and funny as hell. “That song sprang from an idea,” Williams explains. The band was listening to a lot of music from Kompakt Records, the influential German techno label. “There was a trend among DJs in the 1990s to do shuffle beats — they would take a classic ’70s rock beat, like Gary Glitter or Slade, and turn it into a 15-minute drone. It was oddly square, very German, but it had a groove, so we thought it would be cool to bring it full circle, take a techno version of a shuffle and return it to a rock format.”

At first, the song sounded like “a 15-minute krautrock psychedelic jam,” and then Braxton added his wacky, wordless vocal line. “The first time I heard it come out of the speakers in the studio I realized: This is a pop song!” It was catchy and huge-sounding, the perfect thing for a TV theme. Williams says, “We thought maybe when Derek Jeter of the Yankees stepped up to the plate they could play it. Every home run we’d get a royalty check.”

Williams is pretty sure “Atlas” is the main reason the band’s recent 6-week U.S. tour sold out.

“We didn’t know what to expect. We had toured Japan and Europe, but in a way we’d neglected America,” he says. “The crowds were into the set, but when you play that song you can tell a certain segment just came to hear it. It’s weird that it’s turned into this big party song, because we never thought this band would generate something like that. If we had set out to do that, it probably would have sucked.”

Later, they kill Fuji Rock’s huge White Stage audience. The music is pounding, complex and effortlessly enjoyable — postrock for the arena-anthem crowd. Backstage, they’re adrenalized, but not as much as Katoman, who is there basking indirectly in the group’s sudden success. With his one-man operation, he’s no longer big enough to handle Battles’ bigger tours, but that’s OK. Earlier, Williams said the group would be spending one day in Tokyo for promotion “and one day hanging out with Katoman.”

Battles play: Sept. 28, 7 p.m. at Liquid Room and Oct. 1, 7:30 p.m. at Shibuya Club Quattro, both in Tokyo ([03] 3444-6751); Sept. 29, 7 p.m. at Nagoya Club Quattro ([052] 264-8211); Sept. 30, 7 p.m. at Shinsaibashi Club Quattro, Osaka ([06] 6535-5569); all shows ¥5,800 in advance.

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