In the first project, several staffers of the Gurren Lagann anime created eight spinoff shorts that explored the theme of "multiple universes" with background music from the television series.

For Parallel Works 2, a different set of animators use all-new background music and character songs.

Source: ANN

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Other: Tengen Toppa Gurren Lagann
Prequel: Gurren Lagann Parallel Works