They're not very similar to each other since La Corda D'Oro doesn't really involve a romance between two people... but since Ai Shite Knight is about two guys and a girl--- and music, I think La Corda D'Oro is the closest thing to that.
Cute girl, romance, rock band, handsome guys and good music. NANA had all that, but Ai Shite Night did it first. . .over 20 years earlier, too. It was kind of revolutionary for its time. I've been wanting to see this show for several years. It was worth the wait!