i know im personally i guess an outlier when it comes to how i interpret byleth in comparison to the rest of the fandom, but i dont think they are meant to be read as an "emotionless mercenary" at all.
byleth is emotionally stunted, definitely. theyre autistic bad at displaying their emotions via their face. her heart does not beat, the crest stone is what powers her body.
i know that from the outside, byleth seems like a character who is supposed to be emotionless. the characters in the game even treat her so, reacting in surprise when she smiles, or when she cries, but if you pay attention to byleths character, she is clearly an extremely empathetic person.
they care deeply about their students, theyre always there to listen to their problems, whether its helping them out or just lending an ear. they have a sense of humor! though it often falls flat, because nobody expects jokes from them. they like to go around the monastery feeding the cats and dogs. they pay attention to their students in order to know whether they would benefit from criticism or consolation.
she is also quite sociable despite being socially awkward on top of it. she has the spirit and drive to take her students to tea and hold conversations with them. she isnt even shy, she will walk up to a stranger and say hello.
i think byleth is likely one of the most misunderstood characters in the game because most people play as if byleth is supposed to be the player (it doesnt help that the game lets you choose their name. im still bitter over that. we could have had voice lines of characters calling them by their name and not just professor, goddamnit...) but guess what, no matter how you play the game, byleth is the same. hell, no matter what you put for their birthday, its always 9/20, according to jeralts diary. they arent just an empty shell of a character meant to be the player
