The Event from One Year Before - S0.E3

Unaired 23rd canon episode of Clannad After Story. One year before the events of the beginning of the story, Tomoya is beginning his second year, and Nagisa her first time as a third-year student. Nagisa is having trouble making friends as usual, while Tomoya and Youhei are busy being delinquents and carrying out pranks at Kyou's, and inadvertently Nagisa's, expense. After Nagisa is knocked out by a falling metal pan that Tomoya and Youhei had set up as a prank for first-year students, a classmate of Nagisa's finally finds the chance to talk with her and they become friends. Nagisa keeps the banner from the prank (with a message to instill confidence written by Tomoya), because she feels it attributed her to making a new friend.