>>2285693I looked up the kanji and I think it's supposed to be 祝 (congratulations). I think the artist's commentary says "birthday congratulations" (
http://www.pixiv.net/member_illust.php?mode=medium&illust_id=29903637) which is a weird way to say "happy birthday", at least in English anyway.
>>2285703It's a term of endearment. A 2D girl is considered the highest form of being.