Don't have an argument about main character. The main hero will be Beowulf. He and his friends (Cerberus, Nevan and others...) are trying to prevent Mundus' invasion to the human world. Sparda tries to stop them. And the final Beowulf fight versus Sparda will be something like that:
Sparda: Give that to me (He needs Beowulf's eye to seal the portal to the demon world)
Beowulf: No way, you've got your own (even three)
Sparda: Well I want yours too
Beowulf: What are you going to do with all these eyes, huh? No matter how hard you try, you will never ruin our plan
Sparda: You're wasting time!
*Tries to hit Beowulf. Beowulf holds his sword and Sparda holds Beo's fist. Blood of Sparda is shed on Temen-ni-gru's altar*
Beowulf: And we supposed to be friends
Sparda: Friends... Riight
*The fight begins.You've beaten the crap out of Sparda, and then the dialogue*:
Sparda: I was defeated?
Beowulf: Yeah man, s**t happens
*Then Sparda hits Beowulf and Beo hits Sparda. Beowulf falls, but Sparda grabs his eye*
Sparda: I won't let you fall
Beowulf: Let me go, you b**ch
Sparda: Grab my sword!
Beowulf: Can't hold down...Oh f**k!!!!!!
*Sparda stays in the Demon World with Beowulf's eye in his hand. Beo fell in Temen-ni-gru*
Sparda: The gates are closing! You f***ing bastard!
Beowulf: F**k you!
*Gates are closed, Beowulf takes his notebook and writes:
"Sparda sacrifised his own blood..."
sees dead woman:
"...and a mortal priestess to shut portal to the demon world"
Then we see Beowulf talking with his friends*
The end.
How's this?