Korosensei has the appearance of a yellow octopus who is about three meters tall and possessed a large, bulbous head with a large smile that rarely breaks or moves, and small, beady eyes. He uses two tentacles as arms, each having two feelers as fingers, and utilized the rest of seemingly jelly-like limbs - his tentacles - to walk. Korosensei has a pair of hidden nostrils, which make him appear to have four eyes if detected. Due to his constant grinning, his color changes based on his feeling.