Yumeko used to be bullied for being bigger than other girls, but after she almost dies in an accident and awakens with no memories, she decides to turn her life aroundーby living happily in her own skin and even going after the one she loves.
Kei Kikuno attends a vocational school as a student. For her part-time job, she works as a contract killer. She is excellent at her job and never gets scared by anyone. One day, she receives the most challenging request.
Students, including Aoi Nishino, take part in class and sports activity at a prestigious high school. Aoi Nishino is a member of the school's archery club. He practices archery studiously and doesn't socialize much with the other students. His childhood friend Haruka Seno is also a member of the archery club, but she worries about Aoi Nishino. 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 traveled back in time to the Sengoku period. Making things worse, they realize that they are in the time right before the Battle of Okehazama takes place.