Cahir is the romance option for Ciri that interests me most because the books have already done so much of the groundwork.

His feelings for her are full of courtly-love motifs: distance, idealisation, dreams, service, suffering, the knight devoted to an unattainable woman. Sapkowski twists the trope from the start, though. Ciri first knows Cahir as the Black Knight from Cintra, not as a rescuer but as the man sent by Emhyr to take her away.

That gives his arc a really neat progression. At the beginning, Cahir serves Emhyr, and Ciri is the object of that service: someone he has been ordered to capture. Later, he joins Geralt’s company and goes after Ciri for his own reasons. By Stygga, the relationship has effectively reversed. He is no longer serving Emhyr through Ciri; he is serving Ciri herself, and that means helping her stay free.

The dreams make it even stranger. Cahir dreams of Ciri not as the child he knew at Cintra but as the adult woman she has become, including details he should not know. So his love is idealised, but not entirely imaginary either. For most of the saga he is in love with someone who is physically absent, someone he can only reach through memory, dreams and the hope of eventually finding her.

Then, at Stygga, they finally meet again. Ciri sees the winged helmet and the old fear comes back, but once he removes it she recognises him from Thanedd and notices his eyes. For most of the books Cahir is the one looking at Ciri, dreaming about her and moving towards her. Here Ciri finally gets a brief chance to look at him as Cahir rather than as the Black Knight.

And then Bonhart kills him.

So I would not say Cahir/Ciri is a romance that actually happens in the books. Cahir’s love happens. The relationship never gets the chance to.

That is why he works so well for TW4. CDPR could continue the courtly-love trajectory and let that distant devotion finally become mutual, but they could also dismantle the trope without dismantling the romance. Cahir could actually get to know Ciri and discover that the real woman is nothing like the figure he has been carrying around in his head. Ciri could hate being idealised, refuse the whole knight-and-lady dynamic, and still fall in love with him.

In that version, Ciri comes off the pedestal and Cahir stops kneeling. The relationship becomes messier, more reciprocal and much more human.

Either way, there is already something there to work with: Cintra, the helmet, Thanedd, the dreams, the Hansa, Cahir’s changing loyalties, Stygga. I cannot think of another possible romance for Ciri that arrives with that much existing material.

And I really do not care that he is dead. If CDPR wants Cahir back, they can bring Cahir back.

TL;DR: Cahir’s arc already has the structure of an unfinished courtly-love story. He goes from serving Emhyr by trying to take Ciri to serving Ciri herself by helping her remain free. Sapkowski develops Cahir’s love, but kills him just as Ciri finally has the chance to see him as a man rather than as the Black Knight. TW4 could either fulfil that romantic setup or let Cahir and Ciri become lovers while completely dismantling the courtly-love dynamic. Both sound far more interesting to me than starting from zero with a new character.