Sword Saint Jia Pael, that's the name of the predecessor whom Leon apprenticed under.
Decades ago, Jia Pael's strength had reached the Holy Extreme, and whether he has touched the Legendary domain now, no one knows.
Because—he went into seclusion.
The reason for his seclusion was: he wanted to become a Magician.
According to Jia Pael himself, practicing swordsmanship meant always being at the forefront in every battle, ending up sweat-soaked and bloodied with unidentified fluids, and having to train vigorously, which was far from dignified!
Magicians are far more elegant, merely chanting spells from the back and unleashing cataclysmic magic with a wave of the hand, and when out of Magic Power, there's a legitimate reason to just lie down on the ground. Even without training, no one despises him, as a Mage is supposed to be feeble and weak. Is there any profession more elegant than that?
No! No one understands Mages better than I, Jia Pael!
