I prefer Kal'tsit/Gladiia.

I've spoken before elsewhere that Theresa doesn't really FEEL like a character to me; she feels more like an "event" that happened to other characters. A Messianic archetype. The people AROUND Theresa, and the effects she had on them are more interesting than Theresa herself. And as a consequence, that doesn't really give Kal'tsit/Theresa any interesting depth. Despite Theresa meaning so much to Kal, the dynamic itself feels pretty plain and isn't really intriguing to me.

Meanwhile I personally find GladKal more compelling because their dynamic involves someone who's arrogance stems from viewing herself far above other races, being humbled by this one woman who has lived for far too long, and has Seen and Experienced far too much for Gladiia to comprehend. Kal'tsit holds both respect and detachment towards Gladiia while Gladiia is in awe (and perhaps even a small bit of fear) of her. They wouldn't fight over dominance--Kal is too tired and has a complex about exerting her will onto others, while Gladiia has to reconcile deference and her insane top energy towards Kal. Kal'tsit makes Gladiia feel small. She behaves like Kal's guard dog, showing overt concern for her, despite her disdain for land-dwellers. Like yes, Kal'tsit willingly went to jail for the Abyssal Hunters, and she doesn't necessarily show a preference for Gladiia over the other fish, but the combination of Kal's selflessness versus Gladiia's selfishness is tasty.

Also this post: https://dlartistanon.tumblr.com/post/715063285007974400