The time is Taisho. Kiichiro, a pure-hearted student, meets Niu, a mysterious young man imprisoned in a Western-style building on his way to school. Despite the iron bars, the two gradually become close, and as they meet, Kiichiro, who grows in love with Niu, finally invites him to "Let's leave the mansion." However, there is a serious reason why Niu cannot leave the mansion... A pure love story from the Taisho era that expresses the manners and customs of the era with rich emotion.