IU dedicated a song for Sulli at her '2019 IU Concert Love Poem'.

IU and Sulli are well-known friends. At the end of her 4-hour concert, IU's first encore song was "Good Day". After the song, IU said, "There is a friend who I recently became unable to see. I was worried that I would break apart on stage. I prepared this stage thinking that I didn't want to cry. It's been a month since I was able to see her. I didn't want her to see that I was suffering because of her, so I did my best to be strong. I feel better because I think I was able to show her a good stage. Even if she can't come to my non-Seoul concerts, she always came to my Seoul concerts and stayed until the encore stage was over. Usually, she doesn't stay for the second encore song, so I want her to hear this song."

She then sang "Love Poem", the titular song from her 5th mini-album. She added, "Whenever I wrote a song and asked her for feedback, she always asked why things were a certain way. I wrote this song to give strength to people who were having a hard time. I always sing with all my heart, but this time, I'll put even more into it."