Arie Kimura is a pale, long-haired fifth-grader who unsettles her classmates with a fairy tale about a monster said to live in the Nijigahara tunnel. Convinced she must be sacrificed to the creature, seven of them push her down a well and pass it off to the adults as an accident, leaving Arie comatose. Glowing butterflies begin to swarm the town, and the story moves back and forth between those children's last year of grade school and the adults they became.