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 and has been highly regarded as a tuning base by Kazuyoshi Hoshino, a former racer who is known as the 'fastest man in Japan'. In North America, a high-performance version of the NISMO specification is available, and despite its quiet looks, the car's hidden performance is currently being re-evaluated.

The Artifact and The Cube are mysterious relics that were accidentally discovered in Japan during dam construction. Researchers from all over the world have gathered in a Japanese research institute to study these relics, which do not seem to belong to human civilisation, and have been working on them day and night. One day, a huge fireball suddenly appears in the sky above the institute, and the institute is attacked by mysterious robots. In the middle of this, Yukina Shirahane, who was visiting the institute to deliver something her mother had left behind, touches the glowing 'The Cube' in a corner of the lab and unlocks the seal on 'The Cube', which had been closed. Then, a samurai appears...

She is a second-year high school student living in Toyama Prefecture. Her mother is a busy and well-known researcher, but she herself is laid-back and not very good at studies. She is interested in geomorphology and is good at housework and cooking. Her future dream is to go on a Mars expedition.