Ugh, I have a bad feeling about this game. You know how the best thing about Katawa Shoujo was how it was very careful about not turning the girls into silly caricatures of their disabilities, and made sure to treat the subject of handicaps with dignity instead of making fun of it? Unfortunately, it really seems the makers of Missing Stars missed all that.
Well, the game is still in-development, so time will tell. Encouragingly, we do not know what disability anyone has yet. It's been kept under wraps so that the characters are not defined by them. Really, Lena is the only one where you can tell at a glance something is off, and while it is unlikely, it is possible she wears the facial restraint as a rebellious fashion statement, or simply to mislead people and make them think she's a biter.