The dual-monarchy and the day/night split are pointedly framed as load-bearing.
The payoff
(Pending — the significance of the two-king split and the Dogstorm/Cat Viper relationship pays off forward of this window.)
Why this matters
Oda foregrounds an unusual political structure (two kings, divided by day/night) the moment the realm is introduced — a structural tell that the relationship between the two rulers, and the symbolic day/night division, will carry dramatic weight in the Mokomo Dukedom arc.