I think this might be Hayate. She has her braid on the left side of her face (right side for us) which is usually Hayate's style. Then again, the rest of her hair is done up more like Nagi's hair usually is. I'm not gonna change it right now because I want to get other peoples opinions first. Let me know if you think I should change it (with an upvote) or keep it the same (with a downvote) and I'll check back later.
The artist tagged the image Nagi on Pixiv. The artist also draws Nagi's and Hayate's eyelashes differently, so I'm inclined to say its probably Nagi, despite the hair being the mirrored.
The artist also tends to draw Hayate's eyes with a more bluish color, while Nagi's with a more redish/brownish color, which makes me think that the hair was probably just a mistake or for some other reason. Either way, I'd say keep it tagged as Nagi.