Early in the story, the narrator foreshadows the tragic end that awaits Giovanni and thus heightens the story's atmosphere of Gothic horror. After Giovanni's first conversation with Beatrice, which leaves him troubled and apprehensive, the narrator observes:
The wisest course would have been [...] to quit his lodgings and Padua itself at once; the next wiser, to have accustomed himself, as far as possible, to the familiar and daylight view of Beatrice [...]. Least of all, while avoiding her sight, ought Giovanni to have remained so near this extraordinary being that the proximity and possibility even of intercourse should give a kind of substance and reality to the wild vagaries which his imagination ran riot continually in producing.
Here, the narrator's cautionary notes suggest that Giovanni should have ceased to pursue his curiosity about Beatrice as soon as he began to suspect that something was awry. Notably, the narrator's warning takes the form of a list of three that starts with the "wisest course," proceeds to the "next wiser," and ends with what Giovanni should have done "least of all"—which, of course, is the path he ultimately chooses. This triadic structure heightens the reader's sense of impending doom. In this way, the story shows the reader that Giovanni has chosen unwisely—and foreshadows the doom that awaits Giovanni and Beatrice after the former succumbs to his curiosity.
"Rappaccini's Daughter" falls within the Dark Romanticism genre. Dark Romanticism is a sub-genre of Romanticism that emphasizes the importance of emotion and intuition over nature and the fallibility of human judgment. Indeed, characters in the story who choose reason over intuition are duly punished: Giovanni harms his lover and becomes poisonous, while Rappaccini's experiment is foiled. Moreover, Giovanni's rational assessment of Beatrice is proven false, revealing the fallibility of his judgment. Dark Romanticism is also characterized by its fascination with the grotesque and demonic. In the story, this aspect of the genre manifests in Beatrice, the monstrous and toxic result of scientific manipulation of the human body. "Rappaccini's Daughter," then, is emblematic of Dark Romanticism.
This short story can also be described as an example of Gothic fiction. Popularized in the 18th century, Gothic fiction is defined by an atmosphere of fear and mystery, as well as a fixation on the macabre. The Gothic elements of the story are particularly evident in its various descriptions of the setting: Giovanni's new lodgings are "gloomy" and "desolate," and the garden features the "ruin" of a marble fountain. The story's depiction of the supernatural, as well as its horrifying ending, reinforce its categorization as a Gothic short story.