"Believe it or not, it isn't that difficult to awaken a human's Soul Power," Rean said. "Ever since I used a Soul Mark to increase my Soul Power, I've known that I would awaken it regardless of whether I had the mark or not. It's just that it would take longer." One must remember that back then, Rean found out his Soul Power was already increasing because of his Light Element Affinity. The only question would be if he would notice it or not. The arrival on this planet could also be called the trigger for that event, as Rean was made aware of the Soul Power of the Zasfins.
"As I've mentioned before, the Zasfins are nothing more than another branch of the human race that evolved as the years passed. That means all humans have the genes to awaken Soul Power. It's just that their genes wouldn't match the Zasfins. Nevertheless, it would be more than enough for the Bloodline Soul Marks to not be made with their Souls anymore."