Speaking of warrior pairs, Breanna and Eoin seem like they’re in a Romantasy sub-plot. Was that intended?

Aye, it was, but not in the way that traditional Romance Novels are structured. In the first two books, their life challenges make it emotionally difficult to see barriers between them are magical (her geas), class-based (his status as a Gaelic Prince of the Blood versus her lineage), and their shifting roles as Champion and Chief. Then, as co-equal Tuatha Goddess and God. Saying more would spoil the surprise, so root for them!