Kyoko feels unsatisfied with her ordinary days although she has a job and a boyfriend. One day, she meets Nishimori, a man with vacant "dog" eyes. This mysterious encounter is the beginning of her new life as Nishimori's dog. In a closed house, they get deeply absorbed in the strange relationship as "a dog" and "its owner"

September 20th. Sunny. I wonder if it bugs me so much because I can't see it. I've gotten totally obsessed with finding out what's inside that bump. It's all I think about on my way to school, in the bathtub, and when I'm trying to fall asleep at night. I mean, if I could just figure out what's inside that bump, I'm sure I could figure out lots of other things too.