Azura: You are the ocean's grey waves, destined to seek~
Azura: Life beyond the shore, just out of reach~
Zuko: You're doing well, my daughter.
Azura: Are you serious?
Zuko: I am, sweetheart. Would you like to sing in a duet with me now?
Azura: Of course!
Zuko: Hehe, alright then!
A & Z: You are the ocean's grey waves, destined to seek~
A & Z: Life beyond the shore, just out of reach~
A & Z: Yet the waters ever change, flowing like time~
A & Z: The path is your's to climb~

Just like his daughter, Zuko the Suicune was a singer. He was the one who taught her how to sing.
His dedication was admirable and he loved spending time with his daughter, singing their song.