@merkros I've been thinking of a couple of ideas for story arcs for King Bryce, though I only have the beginnings in mind right now.
1. The King's Own Regiment.
An elite, highly trained and proud body of soldiers with strong traditions (Itheria being strong on traditions, as established), but drawn from commoners rather than nobles. In battle and in public, they often go about wearing fierce masks.
Because they are, by tradition, first to battle, they often suffer losses. To compensate for this, every cohort of new inductees pledges together to support their survivors and dependents as a group, and it is an established custom that during their service, all of their wives are held in common, to help support each other during their absence. The regiment may recruit new wives to join a newly inducted cohort.
Bryce goes masked in one of their uniforms to take a sense of his troops and is mistaken for one of the newly inducted cohort. Will he participate in the traditional group send-off?
This arc suggests that Bryce's story will be more militant, following the army, and may repeat his practice of disguising himself as a soldier. Perhaps someone from The King's Own will be promoted and given noble rank and responsibility.
Vessa may be called upon to help improve his disguise. He may also make use of disguise if there are threats of assassination from a rival claimant or a noble who feels Bryce is ruling poorly (war is bad for business, perhaps).
If Bryce sires a child on one of the King's Own's wives, it may be difficult to make a case for parentage given the circumstances. But if a dalliance becomes known, it might be possible, if Bryce has made enough enemies, for Itheria's nobles to force him out and set up a regency, even if Bryce's legitimate line may still be recognized. Or perhaps they will set Bryce's younger sibling up as a biddable substitute, who will have to find their own way to power after the regency council relinquishes nominal power.
Some directions: Bryce may be kicked out as King but retain a lower noble title, or may go to live in exile. If his martial skills are strong, perhaps he will be The King Without A Throne, cutting a path through
(edit: not Luxem) the rest of Motania but sparing Itheria. If he retains the throne, he may have to face difficult choices about who his allies are -- those who helped him in war may not help to keep the peace.
2. The Queenmaker.
King Bryce, young and untried with women, may be fixed up with an older, experienced noblewoman who can teach him the ways of men and women.
First Bryce will face of choice of what woman might be suitable; the Regent may have a suggestion, or perhaps there's an older female relative. Depending on who he chooses, some noble houses or factions in Itheria's royal court may feel favored, others slighted. Some candidates may be explicit agents for their family's interests, or if not the lover herself, someone among her servants. Or perhaps Bryce will pick someone that no faction has any attachment with, someone he knows from when he was younger, a riding instructor, music teacher, storyteller, librarian, or a gentlewoman of his mother's household.
Whoever Bryce picks will have his ear for pillow talk, and may have her own perspective on who Bryce should choose as his Queen. A noblewoman will be able to advocate for a Queen whose political connections are useful, whose temperament is even, and whose family has a reputation for easy childbirth. A social and vivacious lover may advocate for a weak-willed Queen who will let Bryce continue as her lover and hostess for unofficial gatherings. A wise first lover will help Bryce build his own counsel on picking a Queen, acting as a sounding board for Bryce to make his own choice among or outside the proposals the many factions who have one or another reason to prefer their own candidate.
The story arc will probably depend on who Bryce chooses, first as a lover (and whether he keeps her on, or whether this is a short course of instruction), and then which factions want Bryce to be married to, and how soon -- some connections will be more useful after Bryce has proven himself in political, military, or justice matters; you may not want your noble house's name tied to a bad or impulsive king. It might be worth reflecting on past history (where's Bryce's mother from? Was she his father's first Queen?)