This thesis examines the reinterpretation of sex and gender in omegaverse fanfiction. In omegaverse fanfiction, characters from popular culture are written into a parallel gender structure, as alphas, betas, or omegas. Using concepts from fan studies and feminist theory, this thesis analyzes three omegaverse fanfiction stories, asking how they intervene in discourses about sex and gender. It shows how omegaverse fanfiction treats discourses about sex and gender in the same way as it treats the original media texts, mining them for meaning in order to imaginatively transform them. As a result, omegaverse fanfiction can be read as critical commentary of sex and gender. This thesis argues that the speculative mode that is characteristic of the omegaverse genre, makes it possible to explore the premises that underlie understandings of sex and gender without being bound by the strictures of reality. Through this speculative mode, omegaverse fanfiction creates a space where the discourses associated with sex and gender can be treated as a set of building blocks, with which individual authors can examine the inner logic of fictional gender systems on societies, relationships, and situations, examine their consequences, and imagine their downfall. Furthermore, by rewriting these discourses through a narrative, and onto familiar characters, the alpha/beta/omega system works as a node through which to imagine how specific reconfigurations of discourses about sex and gender would play out as lived, situated, meaningful experience. In the stories analysed in this project, the figure of the omega is made to signify female-coded otherness, a personification of the multiple discourses by which women have been (and still are) constructed as other. By writing a male character as an omega, experiences of being treated as other in female-coded ways are imagined to be experienced by a character who represents the male norm. As a result of this double gendering, experienced of female-coded otherness are imported into the universal. Finally, it suggests that omegaverse fanfiction can be read as a kind of ‘low theory’, theory that exists at the margin of formal knowledge formations, creating alternative ways of talking and thinking about sex and gender.