TL;DR:
Luffy - sun god
Shirahoshi - sea god
Loki - forest god
BB - earth god**
All four gods vs IMU, before BB backstabs her.
There is a centuries-long love story, alluded to in various cover stories, including Shanks', and in Thriller Bark as an arc.
Currently, that love story is represented by Shirahoshi (Mosa) and Loki. They will reunite in this world. That's what the entire metaphor is about: land and sea together, at peace, in one piece.
In the previous world, IMU was the Shirahoshi, and her lover was an ancient giant who either:
1. was evil;
1.1. and JB killed him;
1.2. or IMU herself had him killed out of distrust, and turned into the Red Line;
Or,
2. he is sealed away and will don the giant strawhat in MJ to destroy the Red Line.
**Forest God and Earth God are opposite facets of the same concept. Forest represents the life on earth, all its creatures and vegetation. Earth is simply the inert matter, the dirt sapped of any vitality. That's what BB wants: all life to be snatched away and reabsorbed by his anti-existential black hole. Forest instead is the vitality of what populates the earth, even if that vitality can lead to destruction and death--it's the fertile possibility therein lying.
So, Loki's ideology will trump over BB's (which does not mean that Loki necessarily defeats BB in EOS), just like Shirahoshi's will trump over IMU's.
Luffy will just empower them (as a fuel of both energy and positivity), and deal himself with the Final Villain.