One of Maeda's best friends. Gets extremely angry whenever someone mentions his wide forehead. While the only one with a proper girlfriend in the series, they constantly fight and bicker, each accusing the other of infidelity. His father runs a motorbike repair shop and Maeda usually makes Katsuji repair his mopeds and loan him pornographic movies. Katsuji has been best friends with Yoneji since Preschool and, originally, his bully.