The song was first uploaded on March 7, 2008. It was Dixie Flatline's first VOCALOID song and his first big hit, which established him as a popular producer and resulted in him being nicknamed Gemini no Hito(ジェミニの人, Gemini guy) by the Japanese fandom.
Gemini is a song sung by both Rin and Len. The tone and wording of the song is rather vague, but many have taken it as a song about them as twins since Len likens himself and Rin to Gemini in the sky. Throughout the song, Rin sings about how she goes through many troubles throughout her life, with Len coming to her aid and letting her feel as though she is not alone. The song also has references to astronomy and astrology, one time even saying that they were destined to meet 'beyond the night sky'.
Note that Gemini is referring to the meaning "twins" and not the zodiac, though there are references.
This song is featured in several albums, including the EXIT TUNES compilations Vocalolegend and Vocalogemini, Dixie Flatline's album Fragments, and the album "Prism" (a full album of cover songs sung by Asami Shimoda).