Kazuki Suzumoto is divorced and he lives with his 15-year-old son Kouki, who is in a susceptible time. The father feels guilty about his son. Kouki then fails his high school entrance exam. In the spring of the following year, Kouki barely passes his high school entrance exam. Kouki mentions to Kazuki that he likes his father's lunch box. The father and son make a promise to each other. Kazuki promises that he will make a lunch box everyday for Kouki, who promises that he will never skip school.