Yin and Ning are two sisters who have been travelling the countryside together since their town was devastated by the evil Taibai Empire. Zhao, their boyhood buddy, has been enslaved by the Taibai himself, and he exploits his genius for tinkering and inventing to survive as a slave to the Empire's whims. Yin unintentionally discovers a famous sword, which offers her incredible combat powers and lets her to call a magical, mechanical fox spirit named Yun, who is vowed to battle by her side. Meanwhile, Zhao is quickly becoming friends with a strange young girl who may possess significant influence inside the Taibai Empire. As Zhao and the Fu sisters become further entangled in the Empire's battle for supremacy over the land, it will take all of the magic and might that the budding resistance armies can muster to turn the tide of war once and for all.