She is a fourth daughter of royalty with no hope of advancement in station, determined to invoke the promise of aid given to her ancestor generations ago by a powerful wizard when her mother refuses to engage a demon threatening the kingdom.

He is a long-lived exo-socialogist, sent to observe these people but not interfere. He broke that directive once before, many years ago, and now another of them has shown up at his outpost door...

I've never seen a story play with Clarke's Third Law ("Any sufficiently advanced technology is indistinguishable from magic.") like this before. Each chapter alternates POV between the two main characters, so it is half science fiction and half fantasy. Sometimes the same events are told both ways. The story is interesting on its own, but told this way it also becomes a lesson on empathy and understanding.

It surprisingly also became a story about severe depression, persevering through grief and trauma, methods of self care, and how mental anguish can appear from the POV of both those suffering and those around them.

And that will always endear this story to me.