I don't know that I'd call underpowered characters annoying, especially not in the way overpowered characters are, but if you're worried that your character is leaning on one side of the spectrum, it's a pretty easy fix: give them a strength and a weakness. Keep them balanced. Sasha has a pretty significant aversion to aether—that's obviously a weakness—but what is she good at? What strengths does she have that may put her above others? It doesn't have to be something combat-oriented. She could have a silver tongue, she could be quick on her feet, she could have a high tolerance for physical pain as opposed to magical.
I think if you have a character that could be classified as "underpowered" it'd be because that character doesn't have any strengths to speak of. Just like an overpowered character has no weaknesses to speak of. If your character is one of the two, give them some traits or skills that pull them back in the other direction.
I think if you have a character that could be classified as "underpowered" it'd be because that character doesn't have any strengths to speak of. Just like an overpowered character has no weaknesses to speak of. If your character is one of the two, give them some traits or skills that pull them back in the other direction.