Witch gave you access to Dark and Anima magic. Any female unit could reclass into it.
It was great as an anti-mage mage unit, but it was a glass cannon of the highest calibre.
They eventually get the ability to use warp once per turn, which was incredibly useful and worth the squishiness.

I was thinking of combining Dark/Anima Tomes with some kind of bladed weapon: knives, swords, or axes.

The question is how does one accomplish that? There aren't too many tier 1 classes that offer that kind combination. In Fates, I don't believe there are any. It's exclusive to promoted classes, so it may be something I need to work towards. =o