In the 25th year of the Taisho era, the imperial capital of Tokyo. The protagonist, Kuze Tsugumi, was born into a noble family, and decided to marry in order to save her family from decline. At this time, her younger brother was involved in an incident caused by a book called "Rare Things". "Rare Things" are inhabited by the soul and emotions of the author, and can have a huge impact on readers. Kuze Tsugumi used her younger brother's accident as an opportunity to see the emotions of the host exuded by the "rare things" - "spiritual charm". In front of the confused Tsugumi appeared people who claimed to belong to the "Imperial Library and Information Asset Management Bureau" (commonly known as "Otsuki") . Their duties are to collect and manage "rare things", and they entrust Tsugumi to assist in the investigation of "rare things". Although Tsugumi hesitated for a moment, she finally decided to join "Otsuki" and started the investigation of "rare things". This is a story about the fate of a girl who swings like a scale.