Jaki Daigōin, also known as the Emperor of Otokojuku, is the leader of the third-year students and the most powerful figure among the student body at the start of the series. He is a master of his own martial arts style, Daigouin-ryuu, as well as a technique known as Kikou Touhou. His presence is so commanding that he is often perceived as being as large as a great Buddha statue, though this is a manifestation of his overwhelming fighting spirit rather than his literal physical size.

Jaki has maintained his supreme authority within the school for over a decade by winning the Dai Ishin Pa-Lien Seiha tournament three consecutive times. This event is a martial arts competition held every three years, and the champion team gains control over Otokojuku itself. The third-year students operate from their headquarters at the Tendo Shrine, and even the instructors cannot give them orders; only the headmaster, Heihachi Edajima, holds that power. This hierarchical structure means Jaki and his peers function less like ordinary students and more like an immensely powerful ruling council within the school.

In the past, Jaki challenged Headmaster Edajima to a duel but experienced his first and only defeat. This loss was a pivotal moment, as it allowed him to recognize the true extent of Edajima's greatness and his own limitations. Despite his fearsome reputation and tyrannical rule over the underclassmen, this event shapes his understanding of strength. He is a character defined by his immense power and his position at the top, but also by the respect he gains for the one man who could best him. The character has a dedicated spin-off manga, Otokojuku Gaiden Daigouin Jaki, which explores his background in greater detail.