After a peculiar dream about an enigmatic forebear, high schooler Yuuko Yoshida wakes to find herself sprouting demonic horns and a tail. Bewildered by this transformation, her mother discloses a grim family history: their lineage stems from the Dark Clan, cursed to a life of impotence and poverty by their archrivals, the Light Clan's magical girls. To break this ancient curse, Yuuko must locate a magical girl, end her life, and anoint her ancestor's Demon God statue with her blood. Serendipitously for Yuuko, a magical girl, Momo Chiyoda, intervenes just in time to save her from a speeding truck. However, the twist of fate reveals Momo as Yuuko's classmate at Sakuragaoka High, surpassing her in strength and stamina. Moved by sympathy for her feeble attacker, Momo undertakes to mentor Yuuko and unleash her latent abilities. Now, Yuuko must rise to the challenge, pitting herself against her benevolent rival to rescue her kin from the clutches of poverty.