Motoki Tateha has been in a steady relationship with his girlfriend Ageha for a year. They were finally prepared to take their relationship to the next level by having sex, but just as they were about to begin, Ageha dies. According to Ageha's mysterious older sister, this scenario has been repeating indefinitely in a continuous loop. In every version of Motoki and Ageha across all parallel universes, the lovers eventually meet the same fate: Ageha dies when they attempt to make love. Although Motoki could choose to end the relationship with Ageha and thereby prevent her death, their love for one another is too intense. Consequently, Motoki will navigate through all infinite possibilities of their relationship until he discovers the one path that saves Ageha.