The story revolves around Kira and Rei, two high school students. Kira is an extremely introverted artist, and Rei is an outgoing playboy with a frightening violent side. The two start a friendship and eventually a romance after Rei sees a drawing that Kira drew on the back of a map she gave him. However, both Kira and Rei are hiding troubled pasts, and through their relationship they confront their past demons. Masao, a student at Kira and Rei's school, has a connection to Rei's violent past. He enters Kira and Rei's lives to try to force Rei to return to the person he used to be. Based on the manga series "Mars" by Fuyumi Soryo (published from February, 1996 to December, 2000 in Japanese shojo manga magazine Bessatsu Friend).