Character Analysis
Lettie Hatter is Sophie's middle sister. She's super-smart and very beautiful, and unlike Sophie, she's not willing to lie down and just admit that she's doomed to failure because she isn't the youngest sister. Lettie has enough resolve and ambition to switch places with Martha in secret and begin her own witch's training with Annabel Fairfax.
We think we would like Lettie a lot if we got to know her, but we basically never see her speak. Martha is the one whom Sophie visits at Cesari's pastry shop, and Sophie doesn't exactly stop to chat when she spots Howl hitting on Lettie at Mrs. Fairfax's house. However, we do know that Lettie is deeply concerned about her sister. The dog-man reveals that he has come to the moving castle to look after Sophie at Lettie's request.
Lettie's relationship with Howl is definitely worth noting. At first Sophie believes that Howl is pursuing Lettie for her beauty—and Howl obviously reinforces this idea by going on about his "Lovely, lovely Lettie Hatter" (6.99).
But we find out later that both Howl and Lettie have their own motives for spending time together: Mrs. Fairfax encourages Lettie to suck up to Howl just in case he decides to teach her his magic, and Howl speaks to Lettie about Sophie's curse a long time before Sophie realizes that anyone besides Calcifer knows she's not actually a ninety-year-old woman. So this whole Lettie-Howl thing is a total red herring to distract Sophie from wondering about her feelings about Howl.
By the end of the book, we find out that the dog-man who has been so passionately devoted to Lettie is part Prince Justin, part Wizard Suliman. And it's the Wizard Suliman who gets the feelings for Lettie once the two of them settle back into their own bodies.
While we don't know for sure how things are going to work out between these two crazy kids, we see signs that they'll make a good match. Lettie, who is so headstrong and stubborn, appears tongue-tied in front of Suliman: "Now he was himself, it was clear that Wizard Suliman was at least as strong-minded as Lettie was" (21.108). Clearly the Wizard Suliman will challenge Lettie, which is what she has been wanting all along.