The core of the Gransazer lore begins in the distant past. According to the archive’s history, an advanced human civilization was wiped out by a celestial entity known as the Warp Monarch. To protect the future, they left behind "G-Units"—genetic markers and powerful mecha (Chouseishin) buried within the Earth.
Each Gransazer can summon a giant (mechanical beast) that combines with others to form even larger weapons or a final robot. gransazer archive
Chouseishin Leviathan (a giant, dolphin/sea-serpent robot). 3. The Chouseishin and Final Form The core of the Gransazer lore begins in the distant past