In the last part of the fight between Syla and Indra, when they return back to the MC's house, it mentions that Syla had a unique mutation to lightning since her first evolution. In that one moment she overcomes her fear, stops her form from destabilizing, and has the lightning act as fuel for her powers, though the heat does still hurt her.
I think the MC already has that mutation, in the fight against Jake, after his tail gets severed by the HERO weapon with electricity, he mentions how the residual lightning helps him recover. So, I think he just needs to work on finding a way to direct or guide lightning in his body, instead of trying to assume command or control of it.