In the magical world of pandora hearts, one of the main character is Alice which transforms into a black rabbit. She got the nickname from Gilbert Nightray whose always having petty fights with her.(~ ^ O ^)~?

In junjou romantica, Akihiko Usami's nickname is "Usagi-san" and when he makes fun of Misaki of doing ecchi stuffs  with him, Misaki calls him "baka usagi-san". I always love those scenes where misaki blushes and fights over his feelings and totally denying it.

I personally rabbit

A third-year art student, age 21 at the start of the series, specializing in ceramic arts. She is well-known by other students for her pottery and her nicknameTetsujin "Iron-lady" for running 6 km to school every morning to help her dog lose weight. She is depicted as a beautiful young woman, who catches the attention of her male friends and coworkers. Yamada is deeply in love with Mayama, but he does not return her feelings and repeatedly encourages her to find someone else. Later in the series, she is angered by Mayama's sudden protectiveness when he tries to shield her from his former boss, Nomiya. Yamada is close friends with Hagu, who addresses her by first name. At the end of the series, Yamada continues as a graduate student in art, while making pottery for Harada Design.(-x)