In the realm of Rimgarde, a catastrophic clash between two colossal robots decimates humanity, leaving a void in its wake. Fast forward twelve years, Empress Yuinshiel of Enastoria struggles to uphold her rule and the trust of her people. Peace shatters when survivors from Rimgarde resurface with their formidable Regalia Gear, seeking Yuinshiel's sister, Rena. Unveiling Rena as a rare 'Regalia,' capable of transforming into a giant robot and linked to Rimgarde's downfall, thrusts Enastoria into turmoil. Balancing national security and Rena's safety from exploitation, Yuinshiel navigates an escalating global conflict. As she defends her sister, Yuinshiel risks triggering a catastrophe reminiscent of Rimgarde's ruin. Bound by sisterhood, the duo confronts perilous challenges, striving not just for personal survival but for the world's harmony.