Cantor is a romance between Amet, the male protagonist of Thief, and Always Falling, an asexual neuter and longtime romantic partner of Amet's beloved from Thief. Essentially, we get to see the polyamorous V of Thief turn into a full triad. This romance unfolds against the backdrop of strife between Always Falling and its estranged family, when Always returns for its grandmother's funeral.
I enjoyed Cantor even more than the first book in the series, in some ways. As with Thief, Cantor for Pearls is light on conflict. But the characters do face real problems and resolve them through reason and thoughtfulness, and it felt authentic and sometimes heart-wrenching. Some of the problems that were only kind-of-resolved in Thief come up again in Cantor, which is a touch I loved. Because life is rarely "I had an epiphany and now I will never have this problem again". It's usually "I had this epiphany and that settled the problem for a while but now it's back because PROBLEM and AGH". And often we come back to the same epiphany, slightly reframed for the newest circumstances. Some problems, like anxiety and depression and culture clash, are things we must struggle with over and over and over again in new variations.
Since this is a romance between a sexual and asexual character, there's none of the passionate sex that one often reads in modern romance. There is cuddling and some masturbation, however. I liked the way Hogarth portrays Always's physical appreciation of Amet: not in a sexual way, but nonetheless physical and intimate. Overall, the emphasis of the romance is on the way their personalities mesh and their enjoyment of each other's company, which is the thing I like best in a romance. I adore when characters love each other based on what they are like, rather than rooted in physical attraction. I'll rate this one an 8.5.