Esperanto’s role in fanfiction provides a compelling case study of how constructed languages function within digital participatory culture. This article examines the ways in which Esperanto appears in fan-created narratives, both as a storytelling device and as a medium for linguistic experimentation. It explores Esperanto’s use as a futuristic lingua franca in science fiction, a secret or resistance language in dystopian settings, and a bridging language between cultures and characters. Additionally, it considers the phenomenon of fanfiction written entirely in Esperanto, highlighting the language’s use in both translation projects and original narratives. Through an analysis of examples, including Ruĝen: rakonto pri intima socialismo and Now You’re Thinking With Portals! Wait, That’s Knot Right, the article discusses the challenges of linguistic authenticity, particularly when Esperanto is incorporated via machine translation. Furthermore, it examines the expansion of Esperanto fan creativity beyond textual storytelling, as illustrated by La Kanto de Tamar (by the author of this paper), a fan-created song blending science fiction with historical legend. This study ultimately demonstrates that Esperanto’s presence in fanfiction extends beyond mere linguistic play; it functions as a dynamic tool for world-building, identity exploration, and alternative storytelling within contemporary fandom culture.