I'm trying to identify an anime series I watched in 2012-2014.
There is a darkness that has swallowed up a city, which has allowed residents to flee from the city, as nothing can live / breathe in the shadow. The darkness emerged from a girl (long white hair, wears nothing but a white dress to her thighs) when she was small, in a group of 5-ish other children (including her sister who has white hair just to her shoulders)
Several years later the group of 5(ish) children gathered together, training themselves to some kind of soldier in a fierce robot suit, to go into the shadow of the country and fight the monster and the shadow that expands and threaten the others.
The main character who is a boy, I think was in a kind of sibling relationship with the girl in the shadow city and the sister who was trained as a soldier with him, because there the only one who can breathe in the shadow /world.
Saw it online on a site called something with waffleanime
Sci-fi, action, mystik, mecha
I think the series is set in Japan in the future
It's a more modern style of Anime