An enemy!
It was only when the Flame Fiend form was revealed that the radiant knight was able to determine the identity of his 'companion'.
The Flame Fiend's rapidly expanding magma hand had pierced through the knight's armor and flesh, intensely burning in his stomach. The tremendous pain, along with his anger and hatred for the enemy, instantly threw the radiant knight into a berserker rage!
Any other human would have exploded and died if they had been injected with such violent fire energy. However, the radiant knights were well acclimated to ice and fire energies, having handled them for long periods of time. The flames in the knight's body could wound him but not kill him. In fact, he started his counter-attack using the massively increased Strength and Physique from his berserked status.