"How can you be sure that the Flamen Head can't break my spatial power seal?"
"As I said before, your spatial power is exceptional. Not only were you born as a hybrid, but you are also a god's vessel. Even though you will never become a god, you still have a god's life breath. Just like your mother, having a god's life breath means you have a chance to attract the attention of a god to give you his godly seat."
Lord Fane explained briefly that a particular god's vessel did not have to follow that god's path. As long as he succeeded in attracting the attention of a supreme god and giving his godly seat, Jerome could inherit from another god and no longer be able to receive the inheritance of the Chaos God. The same thing could happen to Lionel.
It's just that Jerome and Lionel are the ancient gods' vessels, making it impossible for any other gods who are brave enough to challenge the ancient gods by seizing their vessels.
