Kenji Koiso is a high school student with a crush on a kendo club beauty, Natsuki Shinohara, and a knack for mathematics. His aptitude with numbers earns him a part-time working maintenance on the global virtual reality world, OZ.

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...