Night Time Picnic (2006)

Original title: 夜のピクニック

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.