In a future Shanghai ruled by alien life forms known as Sorui, an operative sent from an undersea city wavers between duty and visions. Winner of the 11th Sogen SF Short Story Award.

In ruined Shanghai, visions and duty converge.

In the Genroku era, scholars acting on Tokugawa Mitsukuni's orders set out to devise a human-powered computer for handling waka poetry. Against an alternate-history backdrop featuring figures such as Seki Takakazu and Yasui Santetsu, the story brings calculation, classical literature, and political ambitions together.

Scholars of the Genroku era attempt to build a human-powered computer to process waka poetry.