Note: This is an extended abstract accpeted by the 2022 International Conference on Social Media & Society. See https://socialmediaandsociety.org/2022-2/2022-accepted-papers/ Abstract: Transmedia and collective storytelling has become one of the most distinctive means of participation in online fandom communities. Meanwhile, networks of scalable sociality afforded by social networking sites have facilitated the engagement of global media prosumers in participatory cultures where collective narratives unfold. During story-telling processes of negotiated readings and creative appropriation of canon, participants of fan culture explore their roles in the fandom and relations to other community members, constantly shaping and re-shaping their understandings of themselves as fans. This study zooms in on a case study of the Dream SMP fandom on Twitter to understand this phenomenon. By qualitatively analysing 200 relevant tweet threads and conducting 20 interviews with Dream SMP fans on Twitter, this study explores how fan identities are situated and defined in the collective making of transmedia narratives on social media.