What would you do?

If one of your best anime friends suddenly "fell out" of liking anime solely because A guy she likes didnt like it. So she didnt want to make him not like her so she gave all her cosplay away and all of her plushies aswell

Tell her, good luck with keeping up the facade. No one should change who they are for another. If she accepted him, he should accept her.

Does this guy like her or is he someone she simply fancies? And he does he hate anime or just not like watching it? Has he watched any anime? I do agree with yaasshat; no one should change who they are but it takes a very strong, confident person to stand their ground. It can be quite difficult when someone wants you to change or like something that they themselves aren't keen on, especially if you're head over heels in love with them. Personally I would stand by her whatever she decided. If it all goes tits up at least you will be there for her...and who knows, something might come of it. They might start going out, he might start liking a particular anime/manga, or he might not be bothered at all at the fact she likes anime.

She says that he likes her back and Apparently he's been taught a very racist outlook so he finds reading manga or liking anime is offensive like "Why would you want to dirty our culture by bringing that in"

Lol no offense to either parties but that just sounds like ignorance. I agree with the other 2 also, you should never change for anyone. She'd be better off finding someone who shares some of the same interest as her. If he actually likes her he should just deal with it honestly. "Dirty our culture by bringing that in" lmao, its in no way doing that not to mention anime/manga has been around for awhile its nothing new. Just be there for her :|. Saying that is like saying anything imported is "dirtying our culture" tons of things are imported on the regular. There are way way worse things(I'm not imply anime/cosplay/manga is bad) but yea you get my point lol.

Here is the thing, there isn't a lot you can do. You can mention once that you wish she wouldn't give up anime but that is about it. If you talk about it too much, she will probably get offended. If you try to reason with her about the guy it probably won't work. I lost a best friend because he asked my opinion about his fiance and I gave it to him. Little over 10 years later and they are divorced and apparently it was a messy relationship with her cheating, etc. In the grand scheme of things though, you are what, 15? Chances are that the friends you have now won't be the same ones you have after going to college. Sounds kinda cold, but it is true.

A girl or a guy shouldn't change to hope the other person would like him/her than. If he or she can't like him/her the way they are than you got the wrong person. Also you shouldn't want someone else to change for you because you'll be together with the shell of the person she/he was before. They'll feel bad because they can't do what they want and if someone is/does/has something you don't like and for that reason you can't love that person ... than again sorry but you just have the wrong person.

Tell him that Xenophobia is a very Japanese response. His circuits will overload with the conundrum and his head will explode. Problem solved.