Sion is basically a charismatic and idealistic young king who to all appearances is nothing if not nearly perfect and flawless. Underneath all that however he has HUGE issues with self-doubt and has generally a crappy opinion of himself due to his life having basically been hell, and not looking to get any better in the long run. He really IS an idealist and kindhearted at heart, mind, and truly wishes to make the world a better place for everyone else's sakes, it's just that he honestly has pretty much zero sense of self-worth and thinks that putting himself through a living hell for the greater good is perfectly acceptable and no more than he deserves anyway.

For first impressions and casual acquaintances though he's VERY good at hiding these issues; the giveaway is more that surely no one could be that calm and pleasant about everything more than actually appearing fake.

Oh, and he's best friends with Ryner and thus chances are high if you interact with Sion Ryner will at LEAST be mentioned if not end up involved somehow. XD