A glimpse into the tradition.
Tsukuyomi occupies a major place in the classical divine family while remaining one of its least narrated members. Kokugakuin University calls Tsukuyomi the second of the “three noble children” and says the kami is usually regarded as male and connected with rule over night. The name is commonly interpreted through the moon and the act of reading or reckoning: tsuki, moon, and yomu, to read. That interpretation fits the importance of lunar phases for calendrical time without requiring a modern fantasy biography to fill the gaps left by the sources.
The birth accounts already show why one tidy version is misleading. In the Kojiki and one alternate Nihongi account, Tsukuyomi appears when Izanagi washes his right eye during purification, paired structurally with Amaterasu’s emergence from the left eye. Other Nihongi traditions give different origins, including birth from Izanagi and Izanami together or emergence from a white-copper mirror in Izanagi’s right hand. The assigned domain varies too: Kojiki gives Tsukuyomi the realm of night, while a Nihongi account assigns the sea, and the main Nihongi presentation places the moon deity in the sky as a complement to the sun.
The contrast with Amaterasu is therefore built through paired imagery - left and right, sun and moon, day and night - but the texts do not give Tsukuyomi anything like Susanoo’s long sequence of conflicts and adventures. In Kojiki, Kokugakuin notes, Tsukuyomi disappears from the narrative after the birth episode. That silence is important evidence. It means later retellings that provide a detailed personality, romance, rivalry, or elaborate lunar mythology are often supplying material the Kojiki itself never gives.