Students, including Nishino Aoi, take part in class and sports activity at a prestigious high school. Aoi is a member of the school's archery club. He practices archery studiously and doesn't socialise much with the other students. His childhood friend Seno Haruka is also a member of the archery club, but she worries about Aoi. One day, thunder strikes the school grounds. After that, the ordinary lives of the students changes drastically. Many samurai descend on the school grounds. It appears that the entire school has travelled back in time to the Sengoku period. Making things worse, they realise that they are in the time right before the Battle of Okehazama takes place. ~~ Based on manga series "Gunjyo Senki" by Masaki Kasahara.