"Remains" is a single from Maurissa Tancharoen and Jed Whedon and was released on July 9, 2009.
During writing and production of "Epitaph One," the 13th unaired episode of Dollhouse (the television series for which Tancharoen and Whedon also write), the two writers felt that a piece of music was necessary over the coda of the episode, but due to budget concerns, they were unable to use a famous or popular song at the time.
Rather, Tancharoen and Whedon wrote "Remains," which can be heard over the episode's final scenes.
However, they wanted the song not to appear too close to the content of the episode lyrically, so as not to distract the viewer with the realization that the song was composed specifically for the episode, despite the lyrics being thematically relevant but not overly specific to the context.
[1] Despite "Epitaph One" having not aired on television in the United States, the episode did air in foreign markets (airdates varied) and was released in the U.S. on the first season DVD set of Dollhouse on July 28, 2009, with the song fully intact.