This article examines notions of authenticity, which have traditionally centered on the individual, and explores instead a view of authenticity that is “reciprocal” (Zahavi 2001; Rokotnitz 2014) and “relational” (Gallagher, Morgan, Rokotnitz 2018). Investigating how children may cultivate a sense of authenticity by engaging in two forms of imaginative projection—make-believe play and fictional stories—I explore how the co-constitution of self and other(s) advances the Existentialist project. Anchoring developmental data, philosophical argumentation, and critical analysis in a literary text written for and about children—J. M Barrie's Peter Pan—I unpack how play and fiction may contribute to authentic self-becoming by fostering social interchange and how this dynamic is made available for interrogation in Barrie's novel. The analysis presented here reveals Wendy to be the heroine of Barrie's novel, reconfiguring its implications for literary scholarship, and also explicates why categories first articulated by Søren Kierkegaard, such as “the single individual” (Fear 67), one's “absolute relation to the absolute” (78), and “witnessing” (104), are still worth pursuing in a post-postmodern twenty-first-century context. Above all, I re-define authentic self-becoming as fundamentally and necessarily relational.