Alright, let's talk Gisena.
To begin with, we should all be aware that we suck dick at social. We look like a freak, we are mentally fucked up beyond belief and we have Curses that make our social even harder. If we want to go in a town, we will likely have to skirt around like a hobo or fight people. Gisena though? She aces that shit. She walks in a town, she can buy and sell everything, get all the freshest info, get is in touch with quest relevant people, talk with authority for us and so on. Remember how we have Geas of Indenture which means that we need to conquer something or kill high profile target? Gisena can help us talk with other people about that. Amazing concept.
On top of this, she scales. She can get more points in her social stuff, and at pretty scary rate given that she is 1/4 Progression. She can get cool Charisma Perks and scale in a way that is completely different that what we do. She can offer us completely different vectors of approach to a problem which would usually be completely impossible for us. And, above everything, she is walking QoL feature that takes care of social stuff so we don't need to invest into it ourselves.
Of course, while her ability to socialize is truly impressive, it's secondary to her actual purpose. You will notice that she is part of specific vote choice - Seals/Sword/Gisena/Retinue. Reason for this is that all those options directly reduce our Curses in various ways, in hope that we will reduce impact Apocryphal would have on our crucial early game. But there is more - Gisena not only Curse diminishment, but one that scales. Forever. As quazi-Progression type she could scale at sealing Curses for millions of years. Remember how in previous quests we were offered choices between reducing Curses and power? With Gisena, we can just take power every time. In time, we could even add Cursebearers to our team simply because we have powerful ability to diminish their Curses on our side. Imagine, for a moment, combat Cursebearer who gets 25% of Progression and his Curses diminished, fighting by our side.
Truly marvelous. And yet, Gisena has uses beyond these - her ability to cancel magic, now, and virtually every esoteric, at some point, would allow her to act as our shield at many points. Value of this should be self-evident already, so I won't waste your time here - yet there are many situations where ability to cancel effects will be of use. Dungeoneering, removing curses and opening seals are but some of uses Gisena could provide outside of "fuck magic".
She has some additional synergy as well - for example, she could reduce our Curse of Indenture so we can bring more people along and then use her social to get us to talk with possible allies for Retinue, making that build that much better. Having access to her magic should do wonders for our Seals, too.