The Nissan Sylphy is the successor to the Bluebird, Nissan's traditional sedan, which was manufactured from 1959 to 2001. This is the third generation of the Sylphy. The Sylphy is an orthodox sedan sold in North America under the name Sentra, but it is also a car with excellent driving performance, as evidenced by the fact that Kazuyoshi Hoshino, a former racer who is known as "the fastest man in Japan," has praised the Sylphy's qualities as a tuning base. In North America, a high-performance version with NISMO specifications is available.

"Artifacts" and "The Cube" are mysterious relics that were accidentally discovered in Japan during the construction of a dam. To study these artifacts, which do not seem to belong to human civilization, researchers from all over the world gathered at a research institute to study and were working on them day and night. One day, a huge fireball suddenly appeared in the sky above the institute, The institute is attacked by mysterious robots. Yukina Shirahane, who was visiting the institute to deliver her mother's lost and found, finds a mysterious robot in a corner of the lab. Yukina touches "The Cube" glowing in a corner of the lab, "The Cube", which had been closed, is unsealed. Then, a "samurai" appears...

She is a high school sophomore living in Toyama Prefecture. Her mother is a busy and well-known researcher, She is a laid-back person and is not very good at studying. She is interested in geomorphology and is good at housework and cooking. Her dream is to go to Mars.