High school student Mifuyu lives in the town of Yomunaga, a community known as the Town of Books that grew around the legendary private library founded by her book-collecting great-grandfather. Her father serves as the caretaker of this vast collection, Mikura Hall, but Mifuyu herself harbors a strong dislike for reading, a result of childhood experiences where adults criticized her literary tastes and she witnessed people trying to exploit her family for access to the library. After her father is hospitalized, Mifuyu is forced to tend to the library and her reclusive aunt Hirune, who lives among the books. During one visit, she finds her aunt unconscious holding a strange talisman bearing the warning: whoever steals this book shall be pursued by the flag of magical realism. A mysterious white-haired girl named Mashiro appears, revealing that a book has been stolen from Mikura Hall, triggering an ancient curse that causes the boundaries between fiction and reality to dissolve. The town begins transforming according to the worlds of various stories, and the only way to restore normalcy is for Mifuyu to catch the thief by entering the books she despises. Guided by Mashiro, who may be a spirit or reflection tied to the library and who can transform into a dog-like creature, Mifuyu journeys through multiple narrative realms. These adventures include a tragic village fantasy and a noir detective story set in a dystopian city where the printed word is outlawed. Within each world, she must solve the riddle of the curse and confront the anomaly representing the thief, all while rediscovering a sense of wonder she thought she had lost.