Page 12 makes it clear to me who's very likely to be the winning girl. Canaan looked great in that shot (almost like a plain wedding dress) with her hand held by Tsukuru. Very main heroine-like. Suzuno, by mere virtue of being the childhood friend, seems destined to lose as per the tropes, unless there is a harem ending or a no romance ending. I kinda feel bad for her. This feeling of mine is only reinforced by Canaan learning Space Magic: that seems super important, and perhaps their ticket to returning back to Earth if it deals with things like teleportation and spatial gates.
Sanya's secret has been teased long enough, even the enemy knows something about her, I'm very curious now...
I don't suppose Black Mist is likely turning into a character soon? Given it has become a lump of flesh rather than a sword. Chances are, it'll get a human-like form that can also revert back to a sword. That would be the predictable expectation, but we'll see.