@reijing Constructive interference that he mentioned is a thing. Obviously the power needed to obliterate a creature isn't able to be produce by a human, even with constructive interference, but at least they're trying to explain it a bit.
@Thirst_420 This would make sense. Alternatively, the devil was actually manipulating everything from the beginning (such as a bee flying on the saintess' cheek at just the right time) because he really did fall in love with her right after forming the contract.