About Jonathan Walker's identity, Jane Aiken must have already guessed it, but the real reason she chose to let go of "hatred" was actually to add another Supreme to the Human Race.
The known top fighters of the Human Race currently include the Three Great Speakers and the True Martial Heavenly King, totaling four Demon God Level combatants, barely enough to contend with the two Great Purgatory Empires.
If Jonathan Walker could kill that Left Demon this time and return to full strength to breakthrough to Supreme, the balance of the top combatants of the Human Race would be broken.
Moreover, Jonathan Walker's true goal is not to be Supreme, but above that, a Civilization Emperor. Otherwise, with his talent, even without splitting into three, he might have made the breakthrough to Supreme in just over a decade.
Therefore, Jack Clark only believed half of what Jonathan Walker told Jane Aiken.
