Izanami-no-mikoto and Izanagi-no-mikoto.
These two deities are said to be the creators of Japan and other gods. So while in the Takamagahara a.k.a the heavens of that time; they were assigned to make something out of the chaotic mass known as earth and to create a few other gods for the newly made lands.
So there was a series of rituals that they had to do to make this happen like while on the Ame no Ukihashi, which means the floating bridge of heaven, they were to churn the sea with a special bejeweled spear and with the water that dripped from the spear islands were formed.
To create more gods its almost like how humans create humans. It involves the union between a man and a women but of course with extra rituals added in the mix. So the two of them got together.
Their first two children was a failure and deformed because they didn’t follow the proper rituals. Their children were Hiruko and Awashima and were not considered deities but devils instead. Learning from their mistakes, they followed the proper rituals and got what they wanted.
But something bad happened during the labor of the fire god, Kagutsuchi. Izanami suffered horrible burns which led her to fall ill and eventually died. So Izanagi buried Izanami on Mt Hiba and her spirit descended to Yomi-no-kuni which is the underworld where all the dead, good or evil would eventually go.
Kagutsuchi was killed by Izanagi who was truly devastated. He even decided he could not part with Izanami that he journeyed to the land of Yomi by himself.
Now, in the Nihon Shoki version,when Izanagi got to the gates of Yomi, Izanami was waiting near the gates but the darkness surrounded her and he couldn’t see anything clearly. He asked her to come back with him but she said it was too late because she had already eaten food from the underworld and now is a part of it…forever.
Though their feelings were mutual. So she said that she could try to ask the lord of Yomi but Izanagi has to wait and never try to look at her at all. Thus they went to her place to rest because its not an appropriate time yet to go to the lord.
Izanagi annoyed at the darkness and wanted to really see his wife, lit a fire. To his surprise, he saw the state Izanami was in. She was rotting, covered with maggots and just surrounded by death. Shocked and in disbelief; he cried out, drewback and ran.
Filled with sadness, disappointment and shame, Izanami wailed at Izanagi for lighting the fire and chased after him. She got some other inhabitants of the Yomi to follow in the chase as well.
He ran as fast as he could but they seem to be gaining up on him. So he made obstacles with his powers. He threw his hairband and wild grape vines grew. He broke the teeth of his comb, threw it again on the ground and this time bamboo shoots grew. Then he even went and urinated near a large tree just to make a river.
So he ran and ran, and finally came to the exit. Once on the other side, he barricaded it with boulders and made it impenetrable.
Now, the two of them standing on opposite sides of the boulder. Izanami shouted at him, saying that if he left her she will make sure to kill one thousand inhabitants of the living every single day! Hearing this, Izanagi replied that he will create one thousand FIVE hundred people every day instead.
And that was their final farewells.
After the ordeal, Izanagi just had to take a bath to cleanse himself. This is when many gods and goddesses, both good and evil were created from each clothing items he dropped on the ground and from his body.
Now the most important ones came when he washed his face; that was when Amaterasu, Tsukuyomi and Susanoo was created.
Want to know the relationship between these 3 gods? Read Amaterasu, Susanoo and Tsukuyomi in Japanese Mythology.