This article unpacks a Nahuatl metaphor based on the kin term hueltiuh, “man's elder sister,” used in multiple sixteenth-century Nahuatl texts and their Spanish derivatives. Through a minute analysis of several Nahua stories, the article identifies various roles described with this term: spies, “toothed-vagina” femmes fatales, heart-eating monsters, and seducers. Applying a method borrowed from cognitive linguistics, it then constructs a model of “man's elder sister,” which explains the application of this metaphor to different contexts. In Nahua stories, hueltiuh is usually a female mediator who throws the male characters off balance, leading to a new status quo. Confusingly, this metaphor often appears where one would expect a real kinship term and in a way that makes identifying its symbolic meaning difficult. These complications have led scholars to see (only) genealogical information in stories concerned with symbolic rather than genealogical relations between elite members or deities. The results presented here allow for refining our understanding of some famous Nahua narratives, such as the one on Topiltzin Quetzalcoatl's abandonment of Tollan. They also invite a rethinking of our views on the Nahua (Aztec) pantheon of gods, whose figurative “family bonds” may, in fact, indicate complex nonkinship relations and dependencies.