Kotoko is a single mother to a young son and quite mentally disturbed. As well as frequent violent fantasies involving horrible ways for her baby to die, she inflicts violence on others, in particular a novelist who falls in love with her, and she self harms herself.
Because of the nature of her mental illness, the viewer is never quite sure how much of this is actually happening,and how much is in Kotoko's head.
It is very effective from that end, as you feel the confusion and disorientation Kotoko herself must feel, but it's not easy viewing, not at all. Time jumps around and it's really hard to pity Kotoko too much, even though you do, because she's ill, but she just does such awful things... And, well...I guess mission accomplished with this one, as I'm sure this is how you are meant to feel. Really a movie to make you feel uneasy and struggle with your thoughts for days after.
Watch if you have nothing better to do.