Added to Hilarious in hindsight. Reason: The picture is from May 2012. Nagisa was introduced (if I remember correctly) around September 2013.

Nagisa was introduced in the third movie and her character was "leaked" to the public a few months before its release, though the fact she was Charlotte's human form

was kept secret until Rebellion was out in theaters. (That said, fans were speculating along those lines from the moment Nagisa first appeared in teaser material.)