In order to become a magus, one first needed to form their foundation and become a rank 9 acolyte. This rank was considered the peak of the mortal stage, and reached the so-called saint realm - the transition phase one had to go through to step into the illustrious magus stage.
Afterwards, one had to strengthen their foundation by successfully erecting the nine pillars in their spirit core. When all the pillars had formed and one reached the peak of rank 9 acolyte, that's when one's spirit core was ready to become the dwelling for the soul - becoming a magus.
It was only when one successfully combined their soul with their spirit core would the core turn into what was known as Spirit Soul. This entity was what defines whether someone was a magus or not and the source of magus' immortality.
