Why is Oma Kokichi short?

Official setting. Oma Kokichi is one of the characters in A New Bullet Breaking V3: Everyone Killing Each other in the New Term, and the theme of "lies" runs through the whole story. His height is short, and he has a keen intuition about everything, which plays a key role in promoting the plot. Oma Kokichi was wearing a white tights and a black and white square scarf. The bottle of purple carbonated drink in my hand is panta.