I think that it depends on the situation. Their culture isn't quite as sarcastic as ours.
The only thing I can think of is "Itai!" which roughly translates to "no way!", but without knowing the specific situation, it's hard to know. [I don't know the japanese characters, I'm afraid.] Sometimes in anime, they simply curse, much like people anywhere else.
Remember also that how anime characters act isn't necessarily the same as how actual Japanese people act. Is your character an actual anime character, or simply an otaku? [An Otaku is someone obsessed with something, usually anime.]
Edit: If you haven't seen it, I suggest watching an anime called "Genshiken". It's about an anime fan club. [Yes; it's an anime about anime.] It may give you some insight and help you fill in the things you are looking to understand.
I realized in the end that the point was that my main character would look up "whatever" on Google translate, rather than actually knowing what the semantic equivalent is.
But I'm definitely going to see if I can incorporate "Otaku" somewhere! And I'm definitely going to look up Genshiken! Thanks so much!
Maybe I'm too late to respond to this, but I live in Japan and I speak Japanese. Maybe the closest thing to "whatever" that I can think of for this situation would be "nandemo ii."
"Ittai" means "ouch."
Thanks! I realized at one point that since the character was riffing on Blood+ and Samurai Champloo, and had almost no understanding of Japanese culture and language, it was appropriate for her to enter "whatever" into Google translate and use that, even if it was wrong linguistically. But I'll definitely store away this tidbit you've given me for future use.
My anime-enthused niece did the drawing for the cover and my sisterinlaw incorporated it into a design. Hoping it uploads when I hit reply
BTW LA Howard, I did buy a copy of Genshiken and watch it. Couldn't get theme song of the faux series within a series out of my head for a long time.
Awesome. :D Ironically, I still haven't watched all of it! My husband and I are -so- back-logged with anime we need to watch that it's ridiculous! Especially now that Netflix has decided to offer a lot of it streamed! XD One of these days, though, one of these days.
BTW, that cover art is awesome! Your family definitely has some varied artistic talents. :D
[Edited for far too many "!".]