No idea but judging from the intro something really bad happened to Miyuki in the past so that might be the reason why Tatsuya looks after her so much.
I'm kinda curious about the things the intro seem to hint at, judging by the part with Erika and pieces of the story so far it seems there'll be some kind of conflict between the different courses and that they're going to battle each other out over the discrimination. Though it seems weird when there's a democratic system in place in the school, then again why is there such open discrimination despite this system.
Weirdest thing so far is that family doesn't seem to matter judging by how people react to the two siblings. Really who cares if you acknowledge her brother or not, it's not like it's going to change the fact that he is her brother and family, which should mean she belongs with him as family and not with a bunch of strangers. Yet the guy takes pride in his family name as if family means something... though I suppose it's overplayed for dramatic effect.