After their father's passing, Sesshoumaru and Inuyasha inherit Tenseiga and Tessaiga, but a third sword, Sounga, emerges. Discovered by Inuyasha in Kagome's time, Sounga, housing a malevolent spirit, poses a grave threat. As they transport the sword to the feudal era, Inuyasha and Sesshoumaru clash over its possession, unaware of its true power and the legacy their father has bequeathed.