A song by a band whose merchandise you've bought - what was the merchandise

I bought a poster! It was at the same concert I referenced earlier this year.

I don't like to repeat the same group or singer on my Crucial Tracks, but there's only one other group I can think of whose merchandise I have bought, and Epik High truly is one of my favorite groups that holds a special place in my heart!

(no reason in particular for this song. It's a good one, but not necessarily my favorite. It was just the first one that came into my head when I thought about Epik High for this prompt. Maybe it's that the song feels nostalgic..)