Wait so let me get this straight, the other world Kokoro didn't met the god and died in the village which indirectly made most of the evil spirits flocking in the village and thus their number is very thin in the city where Reina lived, which in turn made Hikaru's father didn't get possesed by one (I think her mother still left them?), thus Reina can live normally without needing to train as exorcist.
So Kokoro returning alive was what triggered the divergence of two world? That's pretty nasty, it would either Kokoro died or Hikaru died, wonder if a world where both are alive and being friend with Reina existed.