Filia knows a lot of ancient spells to help her fight off demon hybrids like Valgaav, but they simply aren’t enough. Her blasts may not even have much of an effect on Valgaav thanks to the latter’s power ups through the Slayers series. Valgaav proved himself to be a very powerful opponent and he could likely just speedblitz Filia with ease. A single blow would be enough to defeat her. Valgaav wins.
