Ronin
Let's rock, baby!
Unsure maybe make sanctus the third fight and then make the saviour the second last and then maybe bring mundus back in with sanctus for them to merge with the saviour? or possibly have sanctus merge with saviour and then summon some kind of demon to merge with them both lol idk the possibilities are endless but i dont want just sanctus being the last
Maybe make Lucifer/Satan appear as some dark soul stealing Sanctus's body and reforming it into a youthful demonic appearance. Challenges both Dante and Nero.
It turns out that fight was just a test for both of them in hopes that one day Satan will enter the human world to rule over mankind, heaven and hell.