A group of high school students stands at the threshold of adulthood, their final days together slipping away like sand through an hourglass. School, once the center of their universe, is about to become just a memory. As graduation nears, five friends struggle to settle on what comes next, pulled between their own hopes, family duties and social expectations. Sensing that the future will likely send them their separate ways, they plan one final trip together to a hot spring. When one of the girls boards the wrong train and ends up apart from the others, the rest of the group has to work together to get her back.