Obuta is the leader of a youth gang that has a score to settle with Ichigo Kurosaki.
Obuta is a FAT CUNT! THE END
The Lost Substitute Shinigami arc
Obuta leads his entire gang, armed with bats and knives, to the Karakura High School with the intent to settle a score with Ichigo, who broke seven teeth of one of the gang members. He seals off the exit from the school and calls Ichigo out. Instead, the bully is confronted by Uryū who punches another gang member in the face, after the latter mistakes him for Ichigo. Obuta gives the order to attack and the gang members lunge at Uryū. When Ichigo comes in to assist the wounded gang member recognizes him and alerts Obuta. The gang leader yells angrily at Ichigo, but since he interrupted their argument, both teenagers punch him at once, breaking three of his teeth and knocking him out.