I'm just gonna chime in about your story idea, though if you are making a story in the dark magical girl subgenre, a girl in white might contrast nicely with the overall tone depending on where the character starts out. Like, she begins as an innocent but then winds up as a dark and twisted individual? Or was she dark and twisted all along?! That could play with the deception angle. Maybe instead of the magical girl character being deceived, she could be the deceiver for once? Or, other magical girls could've been in on the deception before her... Something to think about.
Also, going back to the design, the red contrasts better with the white, looking more blood-like, if that's the theme you're going for. This could symbolize her underlying violent nature (is that a sword I see?) and also that special time in a young girl's life where... yeahhhh things get messy
. And aren't most magical girl stories thinly veiled coming-of-age tales as well? This could totally work! And I have no clue what your story is about, I'm just getting all of this from your character design, which I really like by the way!! This definitely looks more sci-fi/sci-fantasy too, so you could get into some real cosmic horror type stuff with that. Maybe she's the magical girl version of a space marine?! 
In conclusion, I would read the HECK out of something with a character like this.