Yeah Yeah Yeahs frontwoman Karen O has been easing up on the beer-spewing, stocking-ripping banshee-tornado whirlwind she’s known for unleashing onstage — these days, she just wants to sing some old fashioned love songs. For the past few years, O has been recording lo-fi songs under the name Native Korean Rock, and last night she joined a few friends at Brooklyn’s Union Pool for an evening of ballads fleshed out by little more than a few plucked strings, a guitar strum or two, and her own wrenching voice, delivered with a big, bright-lipsticked smile. (You can hear some of the music on Native Korean Rock’s MySpace page.) Dressed in a sailor suit with dramatic silent-film-star makeup, O looked like the subject of a classic painting: she performed against a blue-sky backdrop, and her band donned navy-themed costumes, playing in a makeshift “boat” with a Korean-flag sail while sound clips of crashing waves and noisy seagulls played softly in the background. O dedicated the end of her first set to “summer love,” before launching into “Indian Summer,” an ode to a romance that goes on longer than planned. No such luck for the set itself: at a mere 30 minutes, it ended much too soon.