The last chapter of Howl's Moving Castle is action-packed, what with the destruction of both the Witch of the Waste and Miss Angorian, and the reversal of Sophie's curse. Of course, since this is a fairytale it makes sense that the evil witch and her fire demon go down. But the interesting thing about Sophie's curse removal is that Sophie notices that her hair is falling "across her face in reddish fair hanks" (21.91) before all of the other curses are removed.
Once Miss Angorian dies, the various body parts that had been distributed between Percival, the scarecrow, and the headless body that Sophie finds in the Witch's fortress all resolve themselves into two men, Prince Justin and the Wizard Suliman. But again—this only happens after Miss Angorian's destruction.
By contrast, the fact that Sophie changes back on her own reinforces the idea that at least part of the curse she's been under is a matter of Sophie's will. It's clearly significant that Sophie finds herself ready to let her curse go once she presses Howl's heart back into his chest. We mentioned in the "Symbolism" section that hearts in this novel—and especially Howl's heart—represent the ability to love truly. Sophie literally holds Howl's heart in her hands when she turns young. Her youth represents her willingness to accept Howl's love now that he is both emotionally and magically capable of choosing to be with her in return.
The other happy endings in this chapter are sketched out pretty briefly. We see that the Wizard Suliman is the one to approach Lettie once his body is back together; he offers to teach her more magic. Remember when Mrs. Fairfax admits to Sophie that she has been encouraging Lettie to lead Howl on so that Howl might teach her more magic? This potential relationship between the Wizard Suliman and Lettie is like the better version of that, where Lettie actually appears to respect and admire the Wizard Suliman. After all, she blushes "fiery red" (21.110) at his offer—a good sign that romance is on the way.
And Calcifer gets the last word. Calcifer decides to rejoin the moving castle's household, as long as he's free to come and go. He clearly likes living there, but he also doesn't much enjoy the drippy weather in Market Chipping (what with being a fire demon and all). Not only does this last gesture from Calcifer prove that he's essentially a decent, sociable guy despite his demonic nature, but it also allows Jones to end the book happily on a small joke, which is totally in keeping with the whole children's fantasy novel thing that Howl's Moving Castle has going on.