These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
YMMV: Hibiki no Mahou
Fridge Horror: All magic requires a sacrifice. What's Hibiki sacrificing?
Although in the beginning it's highly probable that her repeated failures in using magic in the beginning is because that she didn't sacrifice anything yet.