I actually think Aqua is pretty useless. Her abilities are literally goddess-tier. In the hands of a smarter and less unlucky person, it would've gone light years ahead of what she has done so far. She could've killed the Dullahan by herself, become a hero, declared her godhood, and reigned over her own religion. Her abilities are that broken (she friggin tsunami'd a city).

Instead, Kazuma ordered her around just to make minimal use of her spells, and even then she is doing more harm than good. She was actually the reason the Dullahan attacked again. She carried Megumin back from her explosion trips after Kazuma stopped doing so.

I love all these kids.