Dai-Guard: Terrestrial Defense Corp.

Thirteen years after vanishing without a trace, the alien race called the Heterodyne suddenly reappears. To fight them, three employees from the 21st Century Security Corporation are tasked with piloting Dai-Guard - a giant robot once dismissed as useless, now their only hope. The problem is, Dai-Guard is outdated and barely functional. It won't be easy, but even ordinary office workers might just have to become the world's last line of defense.