After re-playing the story a few times, my understanding is this: Jamie's Grandfater (heretofore JG) designed Jamie as the perfect receptable for his soul. It was set that when Jamie was born after JG died, Jamie's soul would be split. Two fully contained entities sharing the same soul, it basically created a new person from the ether. Jaime would live a normal life in the real world, and JG would be a fully realized person but on the other side (Like Mizue ending up being). Cro did the same to Misaki, and that's why Misaki and Kieran (who is also Misaki) are in a similar position. There's some other stuff like Mizue was always supposed to be around, but JG's doings removed her from the initial timeline.