Can anyone tell me what anime this nekomimi girl is from?
This is the character Mito Mashiro, the main heroine from the visual novel/eroge Tayutama: Kiss on my Deity by studio Lump of Sugar. It has a 2009 anime adaptation, but I think the image posted is taken from the VN directly. She is the incarnation of a goddess, and her goal is to bring harmony between humans and a fictional supernatural race called Tayutai. She also falls in love with the protagonist.

Here's a similar picture from the visual novel. It's a slightly different pose, but I think it's clear that it's still her.