Ansatsu Kyoushitsu: Deai no Jikan
Assassination Classroom
Ansatsu Kyoushitsu: Jump Festa 2014 Special
Assassination Classroom: Meeting Time
暗殺教室 episode:0 出会いの時間
Koro-sensei reminisces about his first meeting with Karasuma, where they first butted heads and fought against each other, ultimately coming to respect one another. However, Karasuma eventually points out their actual meeting wasn't nearly as eventful.
(Source: ANN)