As night falls over the academy, the encroaching shadows from Koga bring a new peril to the kunoichi trainees of Iga. Shinobu's closest friend Aya becomes afflicted after a fateful encounter and begins to lose her will, setting the stage for the same affliction to claim Lena. With time running short, the group must infiltrate the Koga Institute's secure laboratories to obtain the only known antidote before the threat spreads further.