Negima!? Magister Negi Magi Episode 18: There`s a Bastard Who Gets All Happy with Secrets, Then Reveals Them, and It Really Pisses Me Off. Chiu-Chiu Is Going to Get Angry Too! Really Mad!
Episode 18 of 26 of Negima!? Magister Negi Magi, aired January 31, 2007, 25 minutes. Available with English subtitles and dub where released.
Episode summary
The Black Rose Baron's identity has been revealed and all of Class 3-A knows it except that the Black Rose Baron doesn't know that the class knows. Konoka and the others decided to keep their knowledge of it a secret from him but will they be able to stop Asuna's big mouth from blowing their cover?