Medaka Box Gaiden: Good Loser Kumagawa

Good Loser Kumagawa takes place two months before Kumagawa transfers to Hakoniwa Academy, and details his time at Suisou Academy. This is the story of Kumagawa's one month-long battle with Saki Sukinasaki, a battle that ended with the closure of Suisou Academy and no winner.

(Source: Medaka Box Wiki)