XIETIAN
Maybe the soul records is a being of Sirius Era. They know who Sirius is and were friends with him. Maybe just Maybe the Soul Records and Sirius met an opponent even they couldn't match and Bai Zemin is the inheritor to solve it.
I was thinking that bai zemin might be able to get all of the ghost emperor soul power as if he killed him. The reason I say this is cause when he died the spear went through both of them and got absorbed almost instantly after he died and maybe cause he is the only person who has done damage to ghost emperor before he died that he would absorb it. ( or maybe it turns into something that the soul evolver owes him