My name is Higashida Takashi. On this summer vacation, my childhood friend Souma Akari, suddenly forced me to go with her to the "Mount Shirokobe" for the sake of learning about our city legend, the "Kubinashi-sama". But ... There is a secret organization "Red Mask Group" who act secretly in the city. There are also rumors about hidden treasures in the "Mount Shirokobe". Then, there is penguin as well ...... Everything is intertwined into one, and move towards the unexpected end. Truly a strange summer story ......