One day, Mizuho, a university student, receives news that her classmate in high school, Origuchi Haruka, passed away. Mizuho doesn't remember being best friends with Origuchi, but apparently, Origuchi told her mother that Mizuho was her best friend. And now, her mother wants Mizuho to help her find the boy Origuchi dated during high school. Mizuho told Origuchi's mother that Origuchi was a very plain girl, and she was never seen with a guy, but her mother told Mizuho that Origuchi got pregnant and had an abortion when she was in high school. Mizuho was shocked, but she still starts asking her other classmates in high school and following the traces Origuchi left behind.