Allu is the older sister of Monica. Even without her instrument, Allu often carries a beat by hitting her hands on various things.
Allu traveled with Monica as rhythmists of the king's military for moral support. They are first seen while playing their instruments for military personnel who were making echo devices. They were doing what they could in order to make money to restore their mother's eyesight. With Monica's help, Rin sings the Song of Healing, restoring her mother's eyesight. Eventually the sisters join Rin and her friends' journey to the capital.