The film follows a group of high school students on a strenuous day-long hike during which they discover new sides of themselves. The story is adapted from author Onda Rika's popular same-titled novel, which earned Onda the Yoshikawa New Literary Writer's Award and the second Honya Award. Yoru no Picnic features a talented young cast including Tabe Mikako and Nishihara Aki who previously appeared in Way of Blue Sky, Ishida Takuya (Rough), Ikematsu Sosuke (Yamato), model Kato Rosa, and Kaku Tomohiro (Hana and Alice). Takako's (Tabe Mikako) 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 (Ishida Takuya), whom she has never spoken to before. Classmates who are unaware of their relationship read something more into their awkward overtures.