This article focuses on the cultural valence of the human-fish (ningyo), a hybrid aquatic creature with a human face and a fish body, in premodern Japan from the eighth to the nineteenth century. Located at the intersection of religious, political, and scientific discourses, the ningyo becomes an exclusive observation point for better understanding the mechanisms of interweaving and mutual fertilization between apparently unrelated semantic fields such as those concerning deities, humans, and animals. Although heteromorphic bodies, here symbolized by the uncanny physicality of the ningyo, are usually dismissed as marginal elements within the broad panorama of relevant intel-lectual productions, this study problematizes this assumption and argues that hegemonic stances are constantly validated, or invalidated, according to their relationships with those on the fringes. Being an interstitial entity, that is, something that lives in the pleats of discourse, the ningyo is characterized by a continuous inclusion within networks of meaning and, at the same time, is doomed to perennial exclusion. This article sheds light on the hermeneutical dynamics that generate the exceptionality of the ningyo, and its never-ending role as a haunting mediator of reality.