This is the J-pop band Puffy AmiYumi. The image is something I had seen in a newspaper or whatever, but I think I was already a fan of the band before I saw the article. The banner also features an English translation of lyrics from one of their songs, "Boogie Woogie No. 5"

I'm not really sure if this banner was in this forum, but it makes the most sense, since it's about a band. Though it does also mention summer, so maybe it should be in the "seasons" category, I dunno.