Tucked away on a remote mountaintop, the Kokoro Library finds it hard to draw in many visitors. Still, it serves as the home for sisters Iina, Aruto, and Kokoro, who view it as their duty to maintain the library in place of their parents. Kokoro has long harbored a dream of becoming a librarian at the library that shares her name, and she does her utmost to keep pace with her older sisters. Because of the scarcity of patrons, the girls mostly spend their time drinking tea, chatting, and reading. Yet, as the number of mysterious visitors gradually rises, Kokoro starts to uncover the strange history of Kokoro Library—a place where small miracles appear to blossom.