Mizu Sakura is a Tokyo elementary student who is transferred to a new school. There, she falls in love with a boy named Hiroshi Nonoichi. The two decide to elope together, fearing that nobody will accept their relationship at such a young age. However, Mizu never shows up for the meeting; a while later Hiroshi learns that she has been transferred to another school. Several years have passed. Mizu is looking for a job and Hiroshi attends college. It looks like both have moved on with their lives. But their past catches up with them when they learn about a mysterious disappearance in the subway system.