Best valentines day gift for a girl who loves anime?

A Death Note. I mean, who doesn't want one of those? Just don't piss her off.

What is a girl? Is that some type of animal?

What kind of anime?

Not quite anime, but pokemon plushies are super cute if she likes them. :3

Artbooks are awesome too, if you know her favourite series. Character sketches and stuff.

Or the manga of the anime, since most anime were based on a manga series?

Penis? Otherwise, check out animes, observe what girls like, maybe buy animes for her to watch with you? Theres a youtube channel called chronexmistia or something that you can check out and see all kinds of new animes you might watch with her, make an all day long anime marathon or something, hell i dont know, dont have a girl. Just buy a little statute or something.

Make a custom story for Everlasting Summer about her, how you met, or your feelings for her (whichever applies)

how about one of those cute figurines from her favourite show like this one http://i00.i.aliimg.com/wsphoto/v3/1659437880_1/10pcs-set-Cute-Puella-Magi-Madoka-Magica-Nendoroid-Petit-PVC-Mini-Figure-Collection-Model-anime-Figure.jpg_350x350.jpg

Get her a tank!

View attached image.

a dildo

maid outfit

Psychoclown's suggestion:

"Banana"

He hasn't said it but I bet he's thinking it.