Great Ninja Onizuka is a fanfiction by Lousy Poet Automaton. The story is a crossover fusing Great Teacher Onizuka, Naruto, Fist of the North Star and Azumanga Daioh. Although the story is thirty-seven chapters long, it was posted all at once on fanfiction.net July 8, 2008.
The basis for the story is that Onizuka Eikichi (protagonist of GTO) is also the heir to the Hokuto Shinken martial arts style (from FotNS) and aided the Yondaime Hokage in defeating the Kyuubi. Eikichi subsequently adopts the orphaned Umino Iruka (the story's protagonist) as his heir. The bulk of the story covers Iruka's time as a chuunin instructor at the Academy and the efforts he makes on behalf of his students, which include the principal characters from Naruto as well as three girls from the Azumanga Daioh manga and anime.