I do feel sympathy for her, and I do mean her, not the myriad spirits the entity "Kalista" has taken, or the Spear of Vengeance that takes them.
She was human, possibly a soldier, that served the kingdom of the Shadow Isles, and one day it all came crashing down. From her perspective, it was a betrayal beyond imagining that damned an entire nation of the innocent and guilty alike, a betrayal from the monarchy she swore to uphold. Noblesse oblige; the duties of royalty and aristocracy, to govern and protect the people.
In one moment of desperation, her world was torn apart. Kalista died with an unquenchable desire for vengeance that the magic of the Shadow Isles twisted for a more sinister purpose, transforming her into a ruthless spirit that takes the souls of invokers and oath breakers, regardless of whether or not they deserve damnation. Now Kalista is an amalgamation of souls, and the woman with whom it all began is nearly lost in the torrent of minds swirling within the specter.
Why I feel sympathy for her is because she does remember who she was, some recognition exists even as more souls are added to the Spirit of Vengeance.
"We - I - must remember."
"Kalista... yes, that was our name."
But for me, the most damning thing of all that tugs at the atrophied strings of my heart, or the black hole where it used to be, is this:
"Why?"
I really think the voice actor did an exceptional job conveying strong emotion behind one word. Such a simple question, but it highlights just how confused, hurt, and angry she is for all that has happened. Kalista wants to know what is the point of so much suffering and loss. For me, that is the clearest moment of Kalista, the person, pushing through Kalista, the Spear of Vengeance.
There remains some semblance of humanity in her, but it is fading away, threatening to disappear. It is a tragedy, losing who you are, bit by bit, until nothing matters, because you no longer exist; a shell something else has taken up residence in.
From a gameplay perspective though, I hate her with every fiber of my being.