Mitsuaki Okubo

Formerly of Kyokuto High School, Okubo (known as Eguriya (Slasher) Okubo because of his vicious use of a knife in fights) of the Madara gang causes trouble for the Oni-Baku when he appears- it turns out he had previously attacked Eikichi and stabbed him in the back during a fight, and wants to finish him for good this time. However, Eikichi gets the better of him in their fight, and beats him to within an inch of his life despite having a broken foot. Wikipedia