Guys these spoilers just made something click in my head, stay with me:
So Loki has the legendary devil fruit of Elbaf, which I believe to be Nidhogg, and Ragnir is Ratatoskr. They are actually going to destroy the world by bringing down the Red Line. Ragnarok will occur, and the whole planet will be submerged by water. Luffy will be on Laugh Tale when this happens and will have to remake the world via The One Piece.
Honestly, given Oda's a big world peace guy, I think the one piece is a toy globe of our real Earth. I can see Oda being sentimental as to make the theme of his story about how we only have this one planet and how special our existence is.
Imu most likely is the only survivor from the last Ragnarok and just managed to stop it in time and control the world in their image instead, clinging onto the hope that they can somehow reverse time to bring all their friends back, which they can’t.
So I think all the good guys we’ve been following are actually the true villains (at least from Imu's perspective) all along, they're the characters who want to bring about the end of the world; “devils”.