1-gatsu ni wa Christmas

During a snowy day just before Christmas, Mizuki Tateno, a girl with a twisted personality, moves into the house next door to university student Fujioka Junsho.
Mizuki says "I hate Christmas". Why does she hate Christmas? Why does she have to live alone in a big house? An incident occurs right after Christmas and Mizuki's past is revealed.

(Source: Wikipedia, translated and edited)