Synopsis
At age seven, Koyomi Hidake chooses to reside with his father after his parents separate. His father is employed at the Japanese Institute of Virtual Science, studying parallel worlds. Through this, Koyomi meets Shiori Satou, whose own divorced father also works as a researcher. They develop a close friendship and share much of their childhood together. As they grow older, Koyomi and Shiori's bond deepens, and they dream of marrying each other someday. Their plans are disrupted when their parents decide to wed, making them step-siblings. Unwilling to accept this, they use their parents' research to flee to a parallel world, hoping to continue their life together. Despite their efforts, obstacles threaten the future they have imagined.
