It’s Japanese for “What”
It’s part of an exchange from an anime that became a meme
The original (in Roman characters so you can sort-of understand) was:
“Omae wa mou shindeiru...” (You’re already dead...)
“Nani!?” (What!?)
Actually, I’m not sure. I’d be willing to bet it’s from Jojo’s Bizarre Aventure, but as I’ve seen exactly three anime (and that wasn’t one of them), I could be entirely wrong.
