Diplomacy
Even though they're happily married, Xander and Corrin still have to abide by their duties as sovereigns of two kingdoms - i.e. they have to hold daily conferences discussing Nohrian-Vallite diplomacy, with said conferences usually lasting for hours on end. Even after they've finished their monarchical duties for the day, they still have to tend to their parental responsibilities raising their two sons. While they enjoy being parents, the lack of "mommy-daddy-alone-time" has taken a toll on the king and queen - meaning that they haven't had the opportunity to have sex in three whole months, and the growing sexual tension between them is agonizing.
There has to be a way to solve this dry spell and carry on with their duties. Perhaps they can even combine sex and diplomacy?
Actually, that sounds like a pretty good idea...
(Smut, Oneshot, Corriander [Xander/Female Corrin], Spoilers for Revelation)
Tartaglia is the Biggest Simp