Haruru's school has a peculiar superstition that claims that couples who happen to spot the bullet train at 6 a.m. together are bound to stay together forever! However, the same doesn't hold true for those who witness the train at 10 p.m. as their relationship is destined to fall apart. Although Haruru is in the early stages of a romance with Nagi, who attends a different school, things take a sour turn when she accidentally glimpses the 6 a.m. bullet train with someone else!