Issei Tsubaki is president of a karate club in Jindai High and Sousuke's rival. He is a skilled martial arts artist, but require thick glasses because of his short-sightness.
He is somethimes accompanied with three identical karatekas, all black belts. Mizuki was infutuated with him in the last episode, much to his annoyance. He only appear in Full Metal Panic?: Fumoffu.