Yura Yamato has just arrived at the high school division of Stella Women's Academy, when Sonora Kashima invites her to join a club called "C³". Sonora is the third-year student who became the new head of this club for military survival games. The other members include two second-year students (part-Japanese Karila Hatsuse and G36K-wielding Honoka Mutsu) and two other new students (Rento Kirishima whose family runs a Japanese sweets shop and the really short Yachiyo Hinata).