Gemini was released in two formats: a limited edition with an exclusive DVD and a regular edition with an exclusive bonus track. The DVD included with the limited edition of the album features a music video for "Gemini-0-eternal" and a making-of documentary for the music video. The album was preceded by two singles: "Senkō", released in August 2010, and "Stargazer:", released in November 2010.
The title of the album refers to a theme of "duality", particularly opposing elements such as light versus shadow and birth versus death. This theme is most prevalent in the trilogy of songs after which the album is named.