She's mean, and she knows it. It's not something she's doing intentionally, really, and if you asked her, she'd say others are far more cruel than she is. After all, there are people she could mention who smile at her face and stab her back as soon as she turns around; isn't that far more malicious than a thoughtless, sarcastic barb? But the people of this valley seem to prefer a poisoned chocolate to the taste of unsweetened cacao.
Which is only to be expected, but she still doesn't like it. So her meanness grows more pronounced, and the few words she spares are bitter and sharp. Her resolve to keep moving grows in her.
The only one she can really stand around here is him. He's the foil to her every movement, her soul's opposite. When she snaps with impatience over the simplicity of this place, he marvels, exclaiming about beauty and honesty. Where she must fight to find a compliment, he struggles to defend himself. There isn't a snip of meanness in him, she realizes, not even the brutal honesty that she prides herself on, but he's not a liar. Rather, it's as if the concept of ill thinking bounces off the side of his head, or maybe impales itself on his hat.
Whatever. The point is, the point that makes her blush and stammer like she never does, is that he isn't mean like she is. He doesn't lie, and he doesn't make sarcastic comments; it's just not who he can be.
So when he tells her he loves her, the miracle of all miracles, she has no choice but to believe him.
AUTHOR'S NOTES
This couple should be relatively easy - why, it's Gustafa and Nami from the DS games and from Wonderful Life!