Nagging is her first song that get to #1 on chart. However, it just a single. IU was never popular with her b-side.
She then exploded in popularity with Good Day.
써클차트 - CIRCLE CHART, 글로벌 케이팝(K-pop) 음악차트
However, her B-side is already doing somewhat great. All of her album is in the top 50.
Then, with You & I, Iu already able to clean the chart with her album.
써클차트 - CIRCLE CHART, 글로벌 케이팝(K-pop) 음악차트
Whereas nowaday, we barely see anyone that can do that?? Even with popular singer like Blackpink and BTS.