back number is a Japanese rock band formed in Gunma Prefecture, known for a melodic pop-rock sound that blends balladry with elements of alternative and indie rock. Active from the mid-2000s, the group gained mainstream recognition in the 2010s through emotionally driven songs characterized by expressive vocals, piano- and guitar-forward arrangements, and lyrical focus on romantic themes and everyday introspection. Their music often features polished production and accessible song structures, appealing to both pop and rock audiences in Japan. The band is associated with the contemporary J-pop/rock scene.