It took me most of the book to realize who Kai reminds me of - Jamie of Lori Foster fame. He's a loner who nobody really understands but everyone is protective - they warned the h off, or tried to. He always seems to show up when he's needed, and… well… Yeah.
The h hears voices. Well, actually, she hears the land. As the H says, her mother is why the Sentinels try their darnedest not to leave fruit behind - just enough power to mess with her head, not enough to really understand why. The h's mother was thought nuts and sent away. She eventually died. I got the feeling that she didn't necessarily consider herself to be nuts, but others convinced her (or was that convicted).
Of course there is the Core messing with things. In some ways, it pushes the H/h together. In other ways, it causes the h to plan to leave. Funny thing - the Core is perfectly ok with using things on people, but they kinda freak out when the land reacts badly to their toys.