In the mythology of the Shinto Religion, the relationship between the father god Izanagi and the mother god Izanami was somewhat complicated.
They started as siblings, then became a married couple, and finally, they turned into sworn enemies.
As for how these parental gods became sworn enemies, it all started with the birth of the fire god, Kagutsuchi.
Being the fire god in the Shinto Religion, Kagutsuchi was engulfed in flames upon his birth.
Izanami's life was in extreme pain during childbirth, and she was scorched so badly that she was confined to her bed and soon died from her injuries.
After Izanami died, Izanagi was heartbroken. After his crying ceased, he drew his renowned divine weapon, the Totsuka-no-Tsurugi known as "Ame-no-Ohabari," and killed his own son, Kagutsuchi.
After killing the fire god, Izanagi, yearning for Izanami, pursued her all the way to the Yomi Country.
Izanami came out of Yomi to greet him, seemingly undifferent from when she was alive.