[She shrugs and tosses the ball up in the air, letting it vanish in a whiff of smoke. Her attention refocuses on Hiro, and she smiles somewhat mysteriously. It's probably not going to be an answer that he likes but...]

It's magic. I just...concentrate, and the flames come. Or bend to my will. I don't know if there is a scientific explanation for it. It just happens, and it has for some time now.