The year is 2027, and the city of Kyoto has undergone tremendous technological advancement. Within the city live two classmates: Naomi Katagaki, a socially awkward and introverted boy; and Ruri Ichigyou, a girl with a cold personality who is often blunt with people. Despite sharing Ruri's love of reading, Naomi is afraid to approach her due to her unfriendly nature. One day, while out on a walk, Naomi witnesses a crimson aurora pierce through the sky for a brief moment before vanishing. Shortly after, he encounters a three-legged crow and a mysterious hooded man, who reveals himself to be Naomi from 10 years in the future, explaining that he has come to change an imminent tragic event that happens to Ruri soon after they start dating. Initially taking his words with a grain of salt, prese