Princess Nine, known in Japan as Princess Nine Kisaragi Girls High Baseball Club , is a 26-episode Japanese anime television series and a three volume manga written and created by Kensei Date.

In Japan, Kōshien (甲子園) generally refers to the two annual baseball tournaments played by high schools nationwide culminating at a final showdown at Hanshin Kōshien Stadium in Nishinomiya, Hyogo, Japan. They are organized by the Japan High School Baseball Federation in association with Mainichi Shimbun for the National High School Baseball Invitational Tournament in the spring and Asahi Shimbun for the National High School Baseball Championship in the summer.