This Nascent Soul is essentially a concentration of a Great Cultivator's Essence, Qi, and Spirit, transformed and elevated, finally crystallized into an extraordinary and potent form.
Therefore, a True Monarch of the Nascent Soul inherently contains at its inception a trace of the Heaven and Earth's true essence. It is a gem forged by the Three Talents - Heaven, Earth, and Man, through lightning and fire, thus rightfully called a True Monarch.
Only then can it, in the event of the physical body's destruction, escape and take possession of another body to be reborn.
This is because the majority of its Essence, Qi, and Spirit are concentrated within the Nascent Soul.
The "Golden Elixir Ballad" states, "The Nascent Soul is rooted in the Golden Core, the Spirit survives with one thought, the Nascent Soul flees from the body..."