Strongest Demigod System

The year is 2055, and the world is being ravaged by monsters born from the veil, called Daemons. The only hope of humanity standing against these monsters are the Demigods who possess Divine Blessings from the Celestials.
Azrael Mortis was a gifted demigod chosen by Thanatos, the personification of death. He possessed extraordinary talent in battle and a work ethic that pushed his body to its very peak, but an unfortunate turn of events when he was only one year old left him with no God Aspect that would allow him to fight against the Daemons. Azrael was already prepared for a life where he would never be able to become the strongest due to his disability.
But as a new chapter of Azrael's life opened, he was presented with an opportunity by Thanatos—one that would grant him the power he had desperately wanted, in exchange for his humanity.
...
"I do not give out opportunities lightly, Azrael. I shall only present you with my hand once, and never again. Take my blade and become my Angel of Death, and in exchange, I shall give you power. All the power you ever wished for and more. Power beyond your wildest dreams. What is your answer?"
"I don't care what I have to do. If I can become stronger, I would even sell you my soul."
"Then may this oath be witnessed by the River Styx. From this moment forward, you shall be known as Azrael, the Angel of Death."