Howl's Moving Castle initially appears to be a lively romantic adventure set in a classic fairy tale world filled with witches, warlocks, shape-shifters, fire demons, and magical castles. These traditional elements are entertaining on their own, as one might anticipate; however, they are also vital pieces of the complex, witty storytelling that Jones is renowned for. Jones's remarkable skill is evident in how these elements also serve as crucial aspects of her theme, as she uses these familiar fantasy tropes to prompt readers to reconsider their preconceived ideas about significant topics like self-identity, personal expectations, the relevance of age in both personal and social contexts, and the various expressions and meanings of love.

The author situates this entire blend within another well-known framework: the eternal battle between good and evil. This conflict is depicted as a struggle between forces that affirm life and individuality and those that diminish or destroy it. Unlike many other fantasies that depict this same conflict—such as J. R. R. Tolkien's The Lord of the Rings (1954-1955) and C. S. Lewis's The Chronicles of Narnia (1950-1956)—here, the conflict is primarily perceptual rather than physical. It hinges on the delicate interplay of truth and illusion, appearance and reality. For instance, while readers are always certain that Sophie Hatter is aligned with the forces of good and the Witch of the Waste with those of evil, there is often ambiguity regarding which side Wizard Howl and his companions truly belong to.

Jones does not see critical issues like the distinction between reality and illusion or good and evil as relevant solely to the fantasy genre. The magical door in Howl's castle opens not only to the fantastical realm of Ingary but also to modern Wales. This is why she places Howl's young nephew, Neil, who shares his uncle's fascination with appearances, firmly within the contemporary Welsh setting. The parallel worlds invite readers to draw connections between a world ruled by magic and one influenced by media, suggesting that both share similarities that can undermine an individual's dignity (as seen in Neil) and authenticity (as seen in Howl). Consequently, the novel is not just a fantasy romance but also a cautionary tale, reminding readers that images and appearances can be easily manipulated, with potentially devastating consequences.