KRONOS (Cronus) was the King of the Titanes and the god of time, in particular time when viewed as a destructive, all-devouring force. He ruled the cosmos during the Golden Age after castrating and deposing his father Ouranos (Uranus, Sky).
Tho I don't believe in strict 1v1 fights, those days are over, so it's gonna be something similar to other war arcs (Wano, Dressrosa, Marineford who didn't have strict 1v1s).