From the book's 2nd page, an avatar of the 2nd Primordial Exotic Demon came out, causing great shock to Azriel.
The Primordial Exotic Demon of Destruction, Olethros! The demon who always drowned himself in battle and destruction.
Azriel was a descendant of this demon since his vampire mother was a descendant of the lineage born from Olethros and the first vampire woman progenitor.
After Azriel was born, his talent and potential quickly caught the eyes of Olethros. At first, Azriel was happy and enthusiastic to receive training from Olethros and fought countless battles against others and got strong. But that changed after some time. Olethros was too harsh in his training because he wanted to quickly make Azriel strong, so he could fight Azriel on equal grounds.
But Azriel got fed up one day and disappeared. Since then, Azriel started indulging himself in a debauchery life that felt way better than his earlier life.