 Sandlot, best known for their work on the "Earth Defense Force" series, first pitched the concept of "Zangeki no Reginleiv" to Nintendo in 2004 alongside a project for the Nintendo DS called "Chōsōjū Mecha MG".Nintendo producer Hitoshi Yamagami was wary of such a large pitch, so he agreed that the developer would make "Chōsōjū Mecha MG" and then go on to "Zangeki no Reginleiv".When production of "Chōsōjū Mecha MG" finished in 2006, the team were given the go-ahead to work on "Zangeki no Reginleiv", though both sides were wary of its scale.