... I know Disney has issues with it... Anime North has had to ban disney items from the Artist Alley because they threatened to sue or something.. (No idea weather this applies to Kingdom Hearts)
Persocom ears (From Chobits) are not allowed either, because the ears themselves are licensed...
.. But if you want to turn it into a business, rather than just a hobby, you probably need permission from the creators..
Fanexpo 2012: Sakura (Infinity) - Tsubasa