Kosei Tsuburaba (円つぶら場ば硬こう成せい, Tsuburaba Kōsei?), also known as Tsuburaba (ツブラバ, Tsuburaba?) | Kosei is a very enthusiastic and competitive individual who holds himself to a high standard as he makes an effort to avoid descending to the level of his rivals. Kosei is described as one of Class 1-B's "common-sense kings".