In the opening scene, InuTaisho is seen delivering a "Meido Zangetsuha" using the Tetsusaiga. In "Inuyasha: The Final Act, Sesshomaru learns that his weapon Tensaiga exists purely as a means of casting out the "Meido Zangetsuha" from the Tetsusaiga, as InuTaisho was never able to master the move. However, not only does InuTaisho unleash a perfectly round Medo using the Tetsusaiga he's also wearing the Tensaiga along with the Tetsusaiga, which should not be possible as it shouldn't exist yet.