Jijii is the homeroom teacher of class 1-D. He always has an armband on his left arm that has different text every time it's shown, the text being anything from the title of the episode to an adage. He is surprisingly lively for his old age and is seen as strange by his students, but the feeling is actually mutual. "Jijii" (爺, "Jijii"?) is used to address a grandfather or an old man in Japanese. He is known for using different "scare tactics" in order to keep his class in order, the first of which was his promise to stand by his students' beds if they were to skip class.

-wikipedia