Kawaguchi’s novel belongs to the genre of time travel fiction, which bends the laws of chronological time to enable characters to visit specific points in the past or future. Characters who traverse temporal dimensions have appeared as early as the eighth century in the Japanese folktale of Urashima Tarō, where the protagonist thinks that he has only spent a few days in the undersea palace of a Dragon God when in truth, 300 years have passed. As scholar Sung-Ae Lee writes, such tales already assume that “time is not one-dimensional but may be two-dimensional, with two strands moving at their own pace and within their own space but with the same characters inhabiting each” (Lee, Sung-Ae. “Adaptations of Time Travel Narratives in Japanese Multimedia: Nurturing Eudaimonia Across Time and Space.” International Research in Children’s Literature, vol. 7, no. 2, 2014, pp. 136-151). Technically, the folktale describes Urashima Tarō falling into a temporal dimension rather than going back and forward in time.

Lee’s research shows that in the 1960s, Japanese cultural media engaged with more diverse notions of time travel. Tsutsui Yasutaka’s young adult novel The Girl Who Leapt Through Time shows the heroine Kazuko’s ability to go back in time and repeat events, on each occasion knowing the outcome beforehand.