Imouto is her!!
Or not.
Really, she isn’t.
It’s complicated. And stupid. I don’t want to explain. But… neither Miyabi nor Konoe is the little sister. So they can go back and whore themselves seduce Shougo:
And Shougo can stop holding back and JAM IT IN into any of the two, or both!!!, since the fear of the imouto isn’t there anymore. But of course, he won’t.
Idiot.
But if he is going to choose just one, Miyabe will not be the one. She triggered the childhood friend flag:
and the childhood promise to marry flag:
THOSE ARE CONTRADICTING FLAGS, MIYABI!!! FFFFFFFFFFFF
Childhood friends lose; childhood promises win out.
This contradiction might spell your doom, Miyabi! D:
There’s also the fact that Konoe is the first girl introduced, her victory is pretty much set in stone!
But even so, Miyabi’s my girl, I’ll support her ’till the end~
Open Your Mind 
And the rest of the harem hasn’t entered the picture yet. There’s a possible chance that a Mashiro-Symphony occurs, and someone else (either the President, or Vice President) that comes in and snatches victory in the last 5 or 6 episodes.
haha that would be hilariously troll-some.