This achievement can only be unlocked in Refrain Mode as you'll be required to use both Excella and Jinas. You cannot unlock this achievement in classic mode.
When outside battle, you can select one member of your active party to be at the center of a B.A.N.D. performance, with each character slightly altering the effect of the songs. You must perform at least one session with each character at the center. Note that Sonia will not be available until later in the game after
The nine characters you'll need at the center are Yuma, Sonia, Kirika, Rinna, Agnum, Marion, Lestin, Excella (Refrain only), and Jinas (Refrain only).