The film follows a group of high school students on a strenuous day-long hike during which they discover new sides of themselves. Takako's high school has a unique tradition. Every year, the school's 1000 students walk 80 kilometers in 24 hours. As this is her final year of high school, Takako decides to work up the courage to talk to her stepbrother You, whom she has never spoken to before. Classmates who are unaware of their relationship read something more into their awkward overtures. ~~ Adapted from the novel “Yoru no Picnic” (夜のピクニック) by Onda Rika (恩田陸).