永久のユウグレ「朝をこころに、一、二と数えよ」

In 2029, seven-year-old Akira Himegami loses his parents and is adopted into the family of Towasa Omagi, who becomes his foster sister. This episode 0, a prequel special to Dusk Beyond the End of the World, follows the two as they grow up and their closeness turns into something more than friendship. Towasa goes on to become a researcher in artificial intelligence, and as public opinion turns against her work, pressure from outside begins to close in on everything the pair have built together.