blondie prince/Sion. But
@luminary mentioned an alternate timeline with Mr. dark hair (and it helps the narration is giving him some importance). Frankly, it all depends on how its going to be written and I admit, I don't ship Mia with Sion, she is after all aware that she's a fake saint, I don't think she's compatible enough with a guy whose righteousness is that high, too many conflicts in ideals. New guy is certainly interesting despite having one line so far, at least it shows he has some self esteem issues, certainly much closer to her personality wise
YOU KNOW WHAT, SCRATCH ALL THAT. Its the new guy apparently. So good news!