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Classes!
A truly wonderful System Function that that the Blood Progenitor had managed to create through the System manipulation. He had even discovered, and explained to Noah beforehand, that he had found the files to create the Classes within the System Seed that Noah had inside his soul.
It seemed that the System Master, the original creator of the System, who had completely abandoned Earth and had not even come back when Noah took it all for some reason, had designed the System based in an already existing one from whenever he came from, which had integrated the Class Function.
When the System was upgraded, the Class Function was unlocked and adapted to Noah's current powers and capabilities. It seems that in the world where the System Master originated from, named Genesis, Classes were able to be changed upon without any cost, but to get power from them, such as Skills and Bonus Stats, Skill Points were needed.