In order to survive the eventual arrival of the "Dusk End," people of the western reaches of the "Land of Dusk" devoted their efforts to rediscover and recreate lost alchemic technologies. Those technologies were then gathered in the alchemy city known as "Central," where research was conducted on how to halt the advance of the twilight. Having learned the newest alchemic techniques in Central, young alchemist Logy requested a transfer to an understaffed town of Colseit on the frontier to make use of his abilities. There he meets Escha, an apprentice girl assigned to the Development Department. Together, the two make a promise to use their alchemic techniques to bring success to the Development Department.
The story follows the two titular women Escha and Chron, whose contrasting personalities are like the sun and moon. The two women are from Terminal, a future post-apocalyptic world that's empty and monochrome. The two women cross worlds and arrive in the present day, which they call Transit. As Escha and Chron experience the light (scenery) and sound (music) of the real world, the future world of Terminal gradually changes into a more vivid world.