This is more a Gauntlet than a boss. Circles five (Anger), six (Heresy), and eight (Fraud) don’t really have bosses. This is as close as you get to a boss in Anger.
I had to cut the ending short because of Youtube’s 11 minute restriction. I guess you’ll have to play through it to see what happens!
Sidenotes: I’m playing through this again on the highest difficulty just to pass time while waiting for God of War 3 and Perfect Dark to come out. This game is amazing. In my opinion, the best hack-and-slash out right now. That may change on March 16.