The Kingdom of Rimgarde was struck by an enigmatic incident twelve years ago, causing widespread devastation. In the present day, Empress Yui reigns over a tranquil and harmonious realm, greatly adored by her citizens, especially her sister Rena. Nevertheless, the unexpected advent of a colossal robot shatters Yui's tranquil existence. Consequently, Yui is compelled to fight tooth and nail to safeguard her empire and her dearest confidant from harm.