The teacher had possibly been teaching at Eitoku Senior High for a number of years, before Tsukushi Makino started going there. He might have been her homeroom teacher.
After angering the F4, Tsukushi was bullied by her fellow classmates. In one such incident, they hid her desk. The teacher realized they were bullying her, despite this he simply told her to go order a new one from the school's front office.
Behind the scenes
He is a minor character and appears in just one chapter.