Korosensei had the appearance of a yellow bipedal octopus. He was about three meters tall, and possessed a large, bulbous head with a large smile and small, beady eyes. He used two feelers as arms, with two fingers each, and utilized the rest of his tentacles to walk with. He wore a black academic dress, a small black square academic cap with a yellow tassel, and a large black tie with a yellow crescent-shaped moon on it. According to Korosensei himself, his nostrils are so small yet when discovered, it seemed that he had four eyes.
The color of Korosensei's face changed depending on his mood, and is as follows:Yellow/Green = Happy, Emotionless/NeutralYellow and Green Stripes = MockeryOrange with a Red Circle = Correct AnswerPurple with a Dark Red X = Incorrect AnswerPink = Sleepy/SmittenPurple = Shock/PanicBlue = SadnessRed = AnnoyanceBlack = FuryPure White = Poker face, A mix of every emotion, or bored.Mild-Yellow = Confused