Izanami vowed to kill 1,000 people per day after being trapped in Yomi. In the Kojiki, she makes this threat after Izanagi flees the underworld and seals its entrance with a massive boulder.
Izanagi had entered Yomi hoping to bring back his deceased wife, who had died after giving birth to the fire deity Kagutsuchi. He became horrified when he saw Izanami’s decomposing corpse, and his escape enraged her. Their exchange explains the continuing cycle of death and birth.
Izanagi answered that he would cause 1,500 people to be born each day, offsetting Izanami’s threatened deaths. The figures are therefore paired: 1,000 deaths and 1,500 births. A common mix-up is to give Izanagi’s counterfigure as Izanami’s vow.