Nestled in a remote mountain setting, the Kokoro Library sees little foot traffic from visitors. Yet, it's the abode of Iina, Aruto and Kokoro- three siblings in charge of the library's upkeep following their parents' passing. Amongst them, Kokoro aspires to become the library's librarian and endeavors to keep pace with her older siblings. With scarce visitors, the sisters find solace in sipping tea, conversing, and devoting their time to reading. However, their routine is interrupted as mysterious guests make their way to the library. Kokoro's curiosity is piqued as she delves deeper into the library's unusual history, where miracles happen in small ways.