Twins Aya and Aki attend what they believe is a birthday celebration, only to find themselves in a grim setting with a mummified hand as a gift. This strange present triggers a transformation in Aya and inflicts wounds on Aki. Their grandfather reveals a dark inheritance plan, pitting the siblings against each other. With the help of the skilled Yûhi and enigmatic Tôya, Aya navigates her newfound powers and the threat to her life. Can her allies protect her from the chaos her own abilities bring?