Was the Vampire Progenitor actually that strong? 

"You said there were certain conditions for the gift, or the system to be activated, what were those conditions?" 

Amaya asked the next question. 

The being stared at Amaya and then Nux, then, after staying silent for a minute, he answered, 

"It was for him to come back." 

"Come back…?" 

Amaya frowned. 

"The condition was for him to come back to the world he originally belonged to. 

His soul experienced countless rebirths, every soul does, that is simply how the universe works, 

You perish, you return to the universe, then you are recreated. 

It is a random process, out of millions of worlds, the world you reincarnate in is chosen completely at random. This is also the reason it is said that once a being returns to the Universe, it is lost.