With the arrival of night, the Koga clan's influence spreads across Iga, posing a fresh danger to the dedicated kunoichi. After a passionate encounter, Yatsurugi Shinobu's loyal friend Mashiba Aya becomes afflicted by a parasitic entity that takes hold of her actions. Kage Lena now risks the same overwhelming compulsion. The sole remedy rests in the Koga Institute's laboratories, prompting a daring retrieval mission to rescue her from the impending fate.