Just Thingking Out Loud... (Spoilers)
Just a thought I was playing around with but here me out. In the last few sentences of dialouge The Samurai says (taken from subtitles) "Aragami..." Turns and looks at the Servant Girl then continues "Who will beat me?" and She replies "I... Will be here to witness it"
At first I believed that he was asking the dead guy and then she replies. But after thinking harder I thought what if she's really Aragami, The God of Battle? After all she has witnessed every battle taken place in the temple and she has probably seen the greatest fights in the history of man,daemon, and other creatures. She's the god of battle and this is her temple, Musachi is just a tengu and the Samurai is a new heavanly being born from the stars.
After reading some posts here most everyone assumes she has no importance but because she remains silent throughout most of the movie I would guess that when she does speak it'd better be important.
Let me know if I have something or just crazy ;)