Poetic diary or Nikki bungaku (日記文学) is a Japanese literary genre, dating back to Ki no Tsurayuki's Tosa Nikki, compiled in roughly 935. Nikki bungaku is a genre including prominent works such as the Tosa Nikki, Kagerō Nikki, and Murasaki Shikibu Nikki. While diaries began as records imitating daily logs kept by Chinese government officials, private and literary diaries emerged and flourished during the Heian period.

Kagerō Nikki is a work of classical Japanese literature, written around 974, that falls under the genre of nikki bungaku, or diary literature. The author of Kagerō Nikki was a woman known only as the Mother of Michitsuna. Using a combination of waka poems and prose, she conveys the life of a noblewoman during the Heian period.