Character Analysis
When you think of the word demon, what usually comes to mind? Chances are decent if you've ever watched anything like Buffy the Vampire Slayer or The Last Exorcism, it's nothing good. In a lot of ways, Calcifer—Howl's fire demon—looks the part of the traditional, stereotypical evil demon, and when Sophie looks into Howl's fireplace and sees Calcifer's face, she comments that "there was no doubt that this one did look extraordinarily evil. Those long purple teeth" (3.41).
And we do see that Calcifer has a highly flexible sense of morality. He admits to Sophie that he's not telling her the entire truth about his contract with Howl, and he basically tells her that those are the breaks. And Howl later admits that he knows that Calcifer is his weak point—he'll never tattle on another fire demon, not even one as evil as Miss Angorian. Mrs. Pentstemmon also says, "Demons do not understand good and evil" (12.56).
But while Calcifer may not be the most reliably good character in the book, he's still deeply likeable. The thing that makes Calcifer so appealing as a character is his vulnerability. He's so proud when he shows Sophie his little flame arm, which he can use to pick up logs from the hearth to eat. And when Howl has to shift the castle from his old house in Porthaven to Sophie's old house in Market Chipping, Calcifer is legitimately terrified:
"I shall have to transfer Calcifer to the house that goes with that hat shop."
"Move me?" Calcifer crackled. He was azure with apprehension.
"That's right," said Howl. "You have a choice between Market Chipping or the Witch. Don't go and be difficult."
"Curses!" wailed Calcifer and dived to the bottom of the grate. (16.47-50)
Calcifer's old-fashioned yell of "Curses!" when he hears that he has to move is funny, and his melodramatic hiding at the bottom of the grate also indicates his insecurity and sense of weakness at being bound to Howl's fireplace by his stupid contract. Unlike Miss Angorian, who really seems to enjoy controlling the people around her, Calcifer seems quite humble and concerned about his safety.
Once Calcifer is free of his contract and chooses to come back and live in the moving castle, our guess that he is a good guy despite his pointy teeth is confirmed: as long as he can choose to come and go, Calcifer is happy to hang out with these crazy folks he's been getting to know in partnership with Howl. Perhaps the real difference between Calcifer and Miss Angorian is that Calcifer has the freedom to choose to do good. Clearly free will is something that this book prizes highly.
Go and Catch a Falling Star
It turns out that fire demons come from falling stars. When a star falls out of the sky (in Ingary, at least) it's time for that star to die. Howl caught Calcifer out in the Porthaven Marshes and felt bad for him, so he offered him a contract to keep him alive in exchange for some of Calcifer's magic.
Not only does this explanation for the background of fire demons give Jones a good excuse for using John Donne's "Song," since the first line is "Go and catch a falling star," but it also might have a symbolic connection to religious representations of demons.
We have no idea if Jones had this in mind at all when she was writing the characters of Calcifer and Miss Angorian, but the most famous demon of all, Lucifer, a.k.a. Satan, is also known as the Morning Star in the Bible. Maybe there's some kind of connection of ideas between the fall of the Morning Star and the falling star/fire demon relationship that Jones proposes in Ingary. Again, we're just throwing this crazy theory out there—it's neat to think about, even if it's a pretty thin connection.