He was one of a number of improbable accordions which rained from the sky one day, onto the Failboat. Callia was only able to save the one, alas. Since then, she has lovingly repaired him more than once, and he has returned the favour by saving her life - also more than once.
Although Calliaphone is extremely fond of music, she has never formally learned to play an instrument. But this problem went away in the face of an improbably sentient accordion. For a long time they enjoyed a healthy busking partnership, in which Cordy did the music and Callia pretended to play, and collected the donations.
All this came to an end a little while ago, in a tragic dodgems-accident at the Bingo Hall Fair. Cordy, horrifically injured by a falling badge-making machine, was eventually restored to working order by Calliaphone. But he has since remained inert and withdrawn, clearly in a state of deep emotional trauma. Callia remains at a loss for how to help him. But Darren has insisted she at least take music lessons herself, because even a non-sentient accordion needs playing.