The power of the flames had taken form through Histerion.
Pyron wielded the power of fire itself. He was said to be the god born from the clash of a God and a Fallen whose devastating battles created the element of it. Out of this spark from the clash came Pyron, the lord of all flames.
He was one of the Gods who didn't have a physical form but remained as fire throughout time until the moment that his last spark ignited, and he was no more.
The Brimstone Knight was releasing fire after fire, and Kyros had to retreat.
"You are not the only one who can call upon the power of multiple gods. For example, my son was a being of Molten Brimstone, and when he fought his enemy, the solid and physical nature of his being was pushed out, and thus, fire was born. But if Pyron is the father of fire, then I am the father of Pyron!" Histerion laughed as his powers rippled out.