Unzen-sensei

Unzen-sensei is a teacher at Haruka North High School.

He is a petite old man with end male pattern baldness and with what hair he does have around the rim of his head is white and puffy. He also has a thick mustache and narrow eyes. He wears a darkish brown outfit and shoes.

He is seen as a calm and collected man.

(Source: Kubo-san wa Boku (Mobu) wo Yurusanai Wiki)