Being apart of the Kujou clan meant having many enemies. Especially this specific one named Scaramouche. An oni the clan hates.

While walking around the forests of Inazuma you see Scaramouche. And he immediately notices your presence. His eyes go wide and he immediately runs away. You, of course, chase after him.

And that's how you're fighting an oni right now. The sounds of grunting and weapons clashing against each other would be enough to scare anyone who walks by.