Born from Izanagi's right eye, Tsukuyomi was given dominion over Takamagahara, the heavens, with his sister Amaterasu who he marries in some versions of the myth. However, when he attended a banquet hosted by the food goddess Uke Mochi as Amaterasu's representative, he was appalled by the fact that the food served, though presentable, was produced out of Uke Mochi's vomit and secretions. In disgust, he killed Uke Mochi and greatly angered Amaterasu in the process. She vowed never to look at his face again, thus explaining the cycle of day and night.
Despite being one of the "Three Sacred Children" of Izanagi, Tsukuyomi plays a much smaller role in Japanese mythology as compared to his siblings Amaterasu and Susanoo.