Ankit

That's what it looks like, and it's not merely a shadowing by Oda, it is very clearly laid out that Yami and Hito are required to beat IMU...this means the last battle is either of the 2 below:

1. Luffy + Blackbeard vs IMU

2. Luffy vs Blackbeard - 1, Luffy gets seriously injured

3. Shanks vs. Blackbeard

4. Shanks dies

5. Luffy vs Blackbeard - 2, Luffy kills Blackbeard in rage over killing shanks