There's been a lot of hand-wringing this year about South Korea threatening to overtake Japan in everything from international diplomacy to technology. In pop music, though, it's already happened. The chart-topping success of now-defunct boy band TVXQ (known as Tohoshinki in Japan) was just a prelude for the current wave of Korean girl groups, who are exposing the wanness of the local talent with their impeccable dance routines, vocal chops and infuriatingly catchy melodies.

After gaining a strong Japanese following via YouTube and import releases, these groups are now making their full-fledged "debuts" here, complete with major-label backing. Kara have scored the biggest success so far, with their Japanese-language "Girl's Talk" selling more than 107,000 copies during its first week of release last month. It's an object lesson in good pop, clocking in at barely over half an hour and dripping with memorable hooks. Half of the tracks are re-recorded Japanese versions of earlier Korean hits, and can be considered improvements only in the sense that they're easier to sing at karaoke. Of the remainder, recent single "Jumpin' " successfully rehabilitates 1980s Europop, while only "SOS" breaks the golden rule of never outstaying your welcome. Tellingly, it's one of two contributions by J-pop producer ArmySling.

4Minute make less of an effort to localize with "Diamond," which compiles new material alongside songs from their first two Korean EPs, only some of them in (heavily accented) Japanese. If Kara tap into the legacy of '80s idol pop, the 4Minute's music is more in step with current Western trends. Vocals are rapped or swathed in autotune, and the arrangements are a splendid mess of hip-hop rhythms and rave synthesizers. "Muzik" and "First" appropriate Daft Punk electro tropes to entertaining effect, while "Already Gone" is a disarmingly sweet slab of effervescent R&B. Even at its most derivative, it's heaps of fun. J-pop makers should probably start taking some notes.