 The keeping of pillow books to record poems, secrets, and encounters  with lovers was a common practice of noble women in Heian Japan.  Although its content is unrelated to the film, a famous example was  written by Sei Shonagon at about the same time as Lady Murasakis  The Tale of Genji which has the honor of being the worlds first  novel. In fact, it has been said that Sei Shonogon and Lady Murasaki  were rivals in the court of Heian.