One day, right before summer vacation, Natsuki asks Kenji to do her a favor -accompany her to her great-grandmother's 90th birthday celebration deep in the Japanese countryside. As Kenji tries to find his footing amongst the boisterous and tightly-knit Jinnouchi clan, receives a mysterious email with a long code and the message: "Solve me." Little does Kenji know what solving that code could lead to...
Based on the award-winning and top-selling animated film by Mamoru Hosoda!