Kagerō Nikki (蜻蛉日記?, The Mayfly Diary) 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.
Kagerō Nikki is often called The Gossamer Years in English, which is the title given to the first English translation by Edward Seidensticker. The term kagerō has three possible meanings: it may mean a mayfly; a heat wave; or a thin film of cobweb, which is the meaning proposed by English Orientalist Arthur Waley.
During the Heian Period, prominent families often collected and compiled their poems in a family collection, or kashū. It is likely that Fujiwara no Kaneie, her husband, asked the Mother of Michitsuna to create such a collection for their family. However, because she decided to add her own experiences along with the poems that she and Kaneie exchanged, Kagerō Nikki emerged. From the outset, the Mother of Michitsuna reveals her concerns by exploring the reality of her condition.
Kagerō Nikki focuses on the development of the Mother of Michitsuna's relationship with Fujiwara no Kaneie ("the Prince") and how these experiences affect her. The diary entries detail events of particular emotional significance, such as when Kaneie visits other women while she stays at home taking care of their son ("the boy"). The Mother of Michitsuna's deep feelings for Kaneie are apparent in the way her words take on a tone of inner anguish as Kaneie's visits dwindle.
In an attempt to find solace, the Mother of Michitsuna makes pilgrimages to temples and mountains of religious importance. She often expresses her desire to become a nun, but the effect that act would have on her son’s future plagues her mind and prevents her from ever taking Buddhist vows.
Towards the end of the diary, she finally reconciles herself to her separation from Kaneie, and determines to devote herself to caring for her son and her adopted daughter.
Kagerō Nikki is said to be a diary, but it is "written in a mixture of styles; the first half characterized more by memoir, the latter half by day-to-day entry." The amount of time that passes between events is sometimes weeks or months.
The Mother of Michitsuna is credited with creating "a new form of self-expression and psychological exploration that expanded the potential of kana prose writing and influenced subsequent woman's writing, including the The Tale of Genji." She achieves this raw, intimate expression by exploiting the first-person point of view allowed by the diary genre. Edward Seidensticker characterized the diary as “a remarkably frank personal confession” that describes “a disturbed state of mind.”  Donald Keene has described Kagerō Nikki as “a self-portrait devastating in its honesty,”  one “written passionately and without a thought to how readers might judge her actions.” 
Another characteristic of the work is the unique way in which the author labels people in her life. For example, in one entry she writes "that 'splendid' personage of Machi Alley" when referring to the woman with whom Kaneie is having an affair. The sarcastic tone reflects the author’s attitude to the person in question: "This method of labeling people shows how very egocentric she was in her dealings with others, defining them solely in relationship to herself."
Kagerō Nikki is the first piece of literature in which Heian social relations and customs are clearly drawn out. The marriage customs in Japan at the time revolved around the idea of "duolocal residence", in which the husband lived in a separate house while the wife stayed at her parents’ residence. Although there was not a structured procedure for divorce, the stoppage of visits signaled the end of a relationship. In expressing her frustration with this system, the Mother of Michitsuna provides valuable insight into the life of married couples during the Heian period. There was also no taboo against the marriage of an uncle with a niece, as seen in the proposed marriage of Tōnori ("the Kami") to Kaneie's daughter.
Born in 935 as the daughter of a provincial governor, Fujiwara no Tomoyasu, the Mother of Michitsuna was a lower- to mid-level member of the aristocratic class. In 954, at the age of nineteen, she married Fujiwara no Kaneie (929-990), who had recently attained the position of captain of the Right Guards. Kaneie later became the Minister of the Right and Regent after his daughter gave birth to Emperor En'yū's son. Although Kaneie continued to climb the social hierarchy, the Mother of Michitsuna’s position as a secondary wife and mother of only one child left her in an unstable social position. Her tenuous relations with Kaneie drove her to consider becoming a nun, but her son and others in her family convinced her to remain in the secular world. She later adopted a daughter of Kaneie's by another woman. Not long after that, the Mother of Michitsuna's sixteen-year-long marriage came to an end. According to her diary, the Mother of Michitsuna devoted her life to her children, and Michitsuna later was able to attain the position of Major Counselor.
The Mother of Michitsuna was known for her skill in waka, classical thirty-one-syllable poems, as indicated by the inclusion of some of her poems in Fujiwara no Teika's anthology Ogura Hyakunin Isshu (or One Hundred Poets, One Hundred Poems, c. 1235) and in the third imperial waka anthology Shūi Wakashū.
In a society in which kana writing was considered a women's activity, inferior to the Chinese writing of educated men, Heian women produced what are today known as some of the most enduring and classical works in Japanese literature. The Mother of Michitsuna speculated that her work would be as ephemeral as "the diary of a mayfly or the shimmering heat on a summer's day," yet she played a crucial role in this legacy.
- Seidensticker, Edward (trans.). Introduction, The Gossamer Years, Charles E. Tuttle Company, Inc., 1964, 1994, p 8.
- Watanabe and Bowring
- Seidensticker, Edward (trans.). Introduction, The Gossamer Years, Charles E. Tuttle Company, Inc., 1964, 1994, p 13.
- Keene, Donald. Travelers of a Hundred Ages, Columbia University Press, 1999, p 29
- Keene, Donald. Travelers of a Hundred Ages, Columbia University Press, 1999, p 26
- McCullough, 1967
- Seidensticker, Edward (trans.). The Gossamer Years, Charles E. Tuttle Company, Inc., 1964, 1994, note 108, p 197
- Shirane, Haruo, ed. Traditional Japanese Literature: An Anthology, Beginnings to 1600. New York: Columbia UP, 2007.
- Watanabe, Minoru; Richard Bowring. "Style and Point of View in the Kagero Nikki."Journal of Japanese Studies, Vol. 10, No.2. (Summer, 1984), pp. 365–384. JSTOR 132143.
- McCullough, William H."Japanese Marriage Institutions in the Heian Period".Harvard Journal of Asiatic Studies, Vol.27 (1967), pp. 103–167. JSTOR 2718385.
- "Fujiwara no Kaneie." Kodansha Encyclopedia of Japan. Online ed. 1993.