Nyx, The Lost Child
At this point Rasoul was already aware that these summonses would come with backstories, demanding his involvement. He had anticipated that even the subordinates he created from the remains of dead beasts and humans would carry narratives that would force him to make decisions, whether he liked it or not.
Master of Eternity already knew about this but decided to conceal it from him since telling him would hinder his destiny. His ultimate goal is to rid the Primal universe of the Dark Ones and their Anti-God who is not known at the moment.
But to do that, he needed an army of his own and what is the best way for a necromancer to raise an army if not raising the dead of his enemies and turning them into his undead soldiers?