Forty-year-old Akane attends the opening of a new art exhibit by her former cram school teacher, Mr. Imai, who has now become a sculptor. Akane notices that Mr. Imai's new sculpture bears a striking resemblance to her middle school best friend, Yukari, who she remembers suddenly transferred out of the school. It even has a distinct scar that Yukari shared with Akane privately.
Wondering what this could mean, Akane reaches out to her old friend, and learns there was something else going on when they were children that she only partly understood. 
Was Yukari just a muse?
Or something with more upsetting implications?