Soku-no-kuni is the yomi in Japanese mythology ruled by the god Amatsu-Mikaboshi. The realm of Soku-no-kuni is a parallel of heaven and reflects the bitterness of the goddess Izanami after she died giving birth to the fire godKagutsuchi and ended up in the Underworld where she remained, trapped behind a boulder that the horrified Izanagi placed there.
Soku-no-Kuni residents are the souls of the sinful, spirits known as Shitidama who are violent beings more demonic in nature than humane. Occasionally these spirits do escape from Soku-no-Kuni and cause havoc on Earth. Due to his contempt for humankind, Amatsu-Mikaboshi does nothing to bring them back.
There are some inconsistencies with the terminology for the name of the realm
The earliest descriptions are derived from Kojiki and Nihongi. In the Kojiki version of the Izanagi and Izanami story, the realm of Yomi No Kuni is described as;
There isn't any mention or referencing to the question of the judgement of the dead or of the souls.
It's not clearly stated who the ruler is. Izanami is called, "The great deity of yomi" towards the end of the story although in the beginning she was just going to ask other deities for advice.
In other Norito, During Ho shizume no matsuri norito, the festival of the appeasement of fire, the Underworld realm aspects are more easily known whereas this isn't so for the Kojiki interpretation. During michi ae no matsuri norito, the festival of the meals offered on the roads, implies the notion of an impure land and source of diseases for both nomenclature Ne No Kuni and Soko No Kuni.
Susano-o refused to rule the ocean from Izanagi's order and chose to go to Ne No Kuni, the land of his mother Izanami. In an alternative of the Nihongi, after he has been chased from takama no hara, the high celestial plain, Susano-o dresses in the guies of mare bito, a voyager coming from the next world to bring prosperity.