The most notable literary device Oyeyemi uses to characterize Harriet is the gingerbread she is constantly baking. It connects with Harriet's past, which helped form her, but also with the present, as Harriet's gingerbread, like Harriet, adapts to the contemporary world: She can, for example, make it without gluten. It symbolizes her personality and how she relates to the world.
For example, we learn much about Harriet herself in the first line of the book from a description of her gingerbread. We learn it
is not comfort food. There's no nostalgia baked into it, no hearkening back to innocent indulgences and jolly times at nursery. It is not humble, nor is it dusty in the crumb.
This tells us that Harriet is a forthright person. This is reinforced when her gingerbread is described, like Harriet, as sincere and strong: unchanging.
Harriet really feels she brings to the Harriet Li/Leigh/Lee brand is a categorical sincerity. Her gingerbread keeps and keeps.
Oyeyemi also uses comparisons to flowers and chocolate truffles to emphasize that like her gingerbread, Harriet is strong and won't fade quickly. Her gingerbread
outlasts all daintier gifts. Flowers wilt and shed mottled petals, mold blooms greenish-white on chocolate truffles, and Harriet’s gingerbread hunkers down in its tin, no more attractive than the day it arrived, but no more repellent either.
The above quote also uses imagery, description that uses any of the five senses of sight, sound, taste, touch, or smell, to illustrate how both Harriet's gingerbread and Harriet herself are durable. In our minds, we can see flowers wilting and dropping delicate petals or chocolate developing "greenish-white" mold. In contrast, we can also see Harriet's gingerbread surviving. The strong Anglo-Saxon verb "hunkers" illustrates the sturdy and enduring quality that Harriet and her gingerbread share.
The gingerbread also symbolizes Harriet's status as outsider, misunderstood and unappreciated by the dominant society. She tries to curry favor by giving gingerbread to insiders:
The biscuit tin fell into the void between Harriet’s outstretched arms and Abigail’s folded ones, and gingerbread tiles spilled out, tessellating with an air of intelligent design.
The "intelligent design" also reflects Harriet's own intelligence.
The narrator tells us explicitly and in a forthright way that seems to reflect Harriet's speech patterns that Harriet is both an outsider and one who would love acceptance:
Still ... does Harriet want in? Fuck yes. Imagine the sense of invulnerability! What must it be like to clock that someone’s staring at you and feel no concern?
We also learn that the "tin" that holds Harriet, her body, appears different from the reality of the dark, thick, strong "gingerbread" she is inside. This is done through imagery that shows that the sweet outside of Harriet—"Bambi-eyed" and "pastel"—is different from the formidable interior:
Bambi-eyed Harriet Araminta Lee seems so different from the gingerbread she makes. If she has an aura, it’s pastel-colored.
Finally, Perdita's impatience with her mother's identification with strangers helps characterize Harriet as engaged with all of life. How others view a character is an important literary device for characterizing them, and Perdita has a running argument with her mother about staying away from helping strangers or taking photos where they took photos. This tells us how Harriet longs to feel connected.