The Japanese Juvenile Fiction Collection began with the discovery of 188 pocket-sized adventure stories from the late Meiji and Taishō periods (roughly 1900-1920) in Penn's East Asian collection, many of which were from the Osaka-published Tatsukawa bunko series. These are cheaply-produced, brittle books that were never intended to last, and Penn's is the most extensive single collection of such fiction in the world. The Penn Librares have been actively growing the collection since 2013 as similar titles become available on the used market. Some of these books are held by no other library in the world, and all public domain volumes in this collection continue to be digitized and made freely available (facsimiles are available via Franklin catalog records).
Adventure, ninja, and samurai stories make up the bulk of this collection, quite a few starring the character Sarutobi Sasuke. Others are biographies of famous warriors or adaptations of Edo tales. The original collection was comprised of two main series: Tatsukawa bunko Tatsukawa Bunmeidō, Osaka) and Shūchin Okawa bunko (Ōkawaya Shoten, Tokyo).