The Combustion Man is a powerful fighter. He has a lot of raw strength in addition to his mastery over fire. That being said, Misaka is quite fast and she has mastered all applications of her electric abilities. Her Railgun is stronger than any of Combustion Man’s attacks and she will be able to zap away at his health in small chunks or keep going for finishing blows. Her supply of electricity will last long enough for victory to be guaranteed. Misaka wins.