So the central conflict... I guess a lot of people would point to the arranged marriage setup with Sylvester and Erna, and the political machinations around him being the 'spare' heir. But for me, the real engine of the story is the internal one. Sylvester is this prince who's been conditioned his whole life to see himself as worthless, a literal 'problem' to be managed. His entire identity is built around being the disposable son.
His conflict is with that ingrained self-perception. Every action, whether it's his initial coldness or his later attempts to protect Erna, is filtered through this belief that he's fundamentally broken and unlovable. The external problems—the scheming family, the dangerous political landscape—are almost just the proving ground where that internal war gets fought. Watching him slowly, painfully realize that he might be worthy of love and a future, that's what kept me hooked.
Honestly, the political stuff is fine, but it's his own head that's the main battlefield.