"Mars Gaiden" is a collection of three Fuyumi Souryo stories. The first, "Namae but Nai Uma" is a prequel to "Marsa," which tells about the first meeting between Rei and Tatsuya and the beginning of their friendship. In addition, they are also represented by other main characters, such as Kira and Harumi. The second and third stories, "Nemuru district" and "1 kartto but kajitsitsa" are online not related to Mars. The first talks about strange relations between the out of the out, a guy who pretends that he is not afraid, and Ayam, a girl with special behavior; On the contrary, the second tells about Nina, who has some family problems, and about Rui, her classmate, who is interested in a close friend of the girl. But what if he is interested in Nina?