Asadal

Asadal (아사달 (阿斯達), meaning "place where the morning sun shines") is a spiritual plain located far beyond the reaches of Soul Society. It is considered the "original land", or even the "birth land." According to Haru Kurosaki, it is absolutely impossible to enter this world from the outside, unless one is of Kawahiru blood.

Overview
Long before even the creation of the physical Universe, there was only a single land. All manners of beings existed here, ranging from Shinigami, Sōzōshin, and even Hollow. Yahweh, going by the One (太極, taiji), was a being that had existed always, and remained the absolute overseer and creator of this land. An incident had arisen where the One had imparted a small diluted amount of his own power in the blood of three families: the Kawahiru, the Kurosaki, and the Asakura.

All was well, but the part of the One that had become the founder of the Asakura had envied the One's power and dominion. He challenged the One, but failed to usurp power, leading him to use whatever power he wielded and created a separate plain below Asadal, being named "Hell". The One, using the name Yahweh more commonly, moved his influence onto another plain, using the name "Heaven" to denote this land, but would soon go by the modern name Soul Society. Several of the Asakura had went with their founder, as several of the Kawahiru and the Kurosaki went with Yahweh. In which time, war began between the two sides, but soon reached a stalemate. The founder, being known by the name "Satan", had decided to wait until his army had grown in numbers large enough so that one day, he would wage war once again. In meantime, human life began in the physical plain, known commonly as the World of the Living. Life would continue and circle within the spiritual and physical worlds, as Asadal was left with its remaining population, flourishing a massive land of their own.