Kanna Amasawa

A story about three sisters struggling to survive in a desolate world surrounded by decaying buildings and red fog. The story revolves around Rin, a girl with an updo. There's also Ritsu, the big sister who has cat ears and is always calm, and Rina, the innocent, cheerful one dressed in a maid's costume. Just what is it that these sisters are after in this mysterious world?