While the title, "Sonny's Blues" would seem to indicate that the story's main character is Sonny, interestingly the greatest change comes in the character of the narrator, Sonny's brother. And, his change is one of perspective, a change that leads to understanding and fraternal love.
Like many older brothers, the narrator pays little attention to his younger sibling, Sonny, in their youth. In an observation of the boys that he now teaches, the narrator describes them much as Sonny was when he used heroin:
All they really knew were two darknesses, the darkness of their lives, which was now closing in on them, and the darkness of the movies, which had blinded them to that other darkness, and in which they now, vindictively dreamed, at once more together than they were ar any other time, and more alone.
The narrator and his brother, paradoxically, are together in a darkness and more alone. As he listens to the boys, the narrator remarks,
Perhaps I was listening to them because I was thinking about my brother and in them I heard my brother. And myself.
When the narrator encounters an old friend of Sonny's who tells the brother that he "felt sort of responsible," the narrator begins "to listen more carefully." Listening to the old friend, the narrator recalls that after he told Sonny about his daughter's death, Sonny had written him, saying how much he needed to hear from his brother.
After this, the narrator stays in touch with Sonny, seeing
the baby brother I'd never known look out from the depth of his private life, like an animal waiting to be coaxed into the light.
And it is the narrator himself who later sits at a table in the dark of the nightclub where Sonny plays the "blues." Like "an animal coaxed into the light," the narrator's spirit connects to the music that Sonny plays. For, after having suffered the loss of his daughter, the narrator, too, knows the "blues," and he begins to listen again to Sonny and, thus, understand him through the commonality of their suffering:
All I know about music is that not many people ever really hear it. And even then, on the rare occasions when something opens within, and the music enters, what we mainly hear...are personal, private, vanishing evocations. But the man who creates the music is hearing something else, is dealing with the roar rising from the void and imposing order on it as it hits the air. What is evoked in him, then, is of another order, more terrible because it has no words, and triiumphant, too, for that same reason. And his triumph, when he triumphs, is ours.
As he listens to his brother play, the narrator begins to understand his own troubles as he watches his younger brother live and then play "the blues"--his triumph is the narrator's triumph. At the end of the story, a girl brings a Scotch and milk for Sonny, a drink the narrator describes as "like the very cup of trembling," from the Biblical book of Isaiah. A a symbol of the suffering and problems that Sonny has experienced, this "cup of trembling" reminds the narrator of his own troubles. In a moment of truth, the brother comprehends that Sonny, through music, turns his suffering into something of worth.