Unuseless Cyborgs: Spiral Posthumanism and Popular Culture in Japan's Ushinawareta Nijunen (1990-2010) examines contemporary American posthuman theories (theories that challenge humanist accounts of embodiment, agency, subjectivity and humans' relation to the environment) through the lens of an emerging critical subjectivity in Japanese popular culture during the Ushinawareta Nijunen (The "Forgotten Decades"). This dissertation creates a conversation between contemporary Japanese popular culture from 1990-2010 and American posthuman theories in order to identify a strand of Japanese subjectivity that straddles the line between liberal humanism and a transhuman post-subjectivity (that emphasizes human entanglements with the non-human). In the absence of a developed Japanese critical discourse of posthumanism, this project adapts American posthuman theory for a Japanese cultural context, exploring the nascent forms of subjectivity revealed in Japanese cultural texts during these decades. These forms, I argue, are critical of Japan's conventionally sanctioned subjectivity in this period, which emphasizes individuality, efficiency, and autonomous thinking. In addition to analyses of Haruki Murakami's short fiction and Junji Ito's horror manga, Uzumaki, this dissertation introduces the Japanese product Chindogu (quirky inventions created to be specifically "unuseless") to American theoretical discourse and is the first to analyze the ways they contribute to a specifically Japanese posthuman discourse during the Ushinawareta Nijunen ("Forgotten Decades") period that I argue is best exemplified in the spiral form.