The 100 Girlfriends Who Really, Really, Really, Really, Really Love You - Vol. 20 Ch. 168 - Rentarou Snapshot Swap Party

[Deathhappens]

A ninja girlfriend, she's been there all along but nobody's ever noticed! Probably hidden in the background of a bunch of crowd shots in past volumes too, no doubt.

I've been binging the manga so I got the joke immediately but man, it IS pretty creepy the way she snuck into the meeting like that.