That anime was my first intro to the 'Silent Witch' universe, and I feel like I've got a decent handle on the cast now. The obvious center is Monica Everett herself—she's the 'Silent Witch' of the title, a royal guard magician who's cripplingly shy and can barely speak above a whisper, yet holds the title of the kingdom's Seventh Mage. Her social anxiety is so severe it's painful to watch sometimes, but her internal monologue and sheer magical power are fantastic. She's basically a walking, blushing contradiction: a national-level protector who'd rather be hiding in a library.
Then you've got Felix, the Crown Prince she's assigned to guard. He's sharp, observant, and seems to enjoy poking at Monica's walls just to see her panic, though it's clear he's fond of her in his own way. His valet, Cyril, is another key piece; he's intensely loyal to Felix and deeply suspicious of Monica at first, which creates a nice tension. I find myself paying more attention to the secondary characters, though. Lana, the loud and brash daughter of a duke, is a great foil for Monica. Her attempts to befriend Monica while being completely oblivious to her true role are both funny and kind of sweet. And you can't forget the headmaster of the academy, who seems to know more than he lets on. The show does a solid job of making even the side characters feel like they have their own agendas.