The United Nations Kurobe Research Institute was founded in Japan around the turn of the century to explore an ancient relic uncovered during the construction of the Kurobe Dam. Scientists from across the globe have congregated in the facility to examine the item, while their children attend Mt. Tate International Senior High School. Yukina Shirahane, a reclusive high school student, is the facility's top scientist's daughter. Yukina solves a piece of the artifact's puzzle while visiting her mother in the facility. Kennosuke Tokisada Ouma, a young samurai from the Sengoku era, appears in front of her, much to her amazement. As a menace from space looms, Yukina, along with Kennosuke, finds herself defending Earth.