dtgreene: There's actually a decent number of classic JRPGs that do this.
Dragon Quest 2: All the main characters are royalty. (Some later games in the series also have the main character as royalty, but that often isn't revealed until later in the game; DQ2 you're the prince right from the start.)
Final Fantasy 5: One of your party members is the princess of the kingdom, but that's not even the whole story here. (Some of the other Final Fantasy games have princes or princesses as party members, but generally only for a small-ish portion of the games.)
Romancing SaGa 1: Albert is the son of royalty.
Romancing SaGa 2: You control the emperor/empress, and once they die (or a timeskip appears) you get to choose an heir.
SaGa Frontier: I *think* that Asellus is a princess, but it's complicated (and also queer, which is unusual for the time the game was made).
SaGa Frontier 2: Gustave is of royal lineage, but is kicked out after it's discovered he has no anima and therefore can't use magic.
Sword of Hope 1 and 2: You're a prince here.
Worth noting that some of these situations involve the king/emperor (the main character's father) becoming corrupt or going missing.
I forgot it was a common JRPG trope, especiall an SE trope. I think the Dragon Quest/Dragon Warrior games might've done this to some degree, but Final Fantasy is notorious for this. Final Fantasy XV did an amazing job in this regard, crushing the usual tropes. We also have the Fire Emblem series, too, as well as many of the knockoffs like The Battle for Wesnot.