The protagonist is an middle-aged man often referred to simply as "Ojisan" (Uncle). Unlike typical anime protagonists who are young, handsome students or mysterious transfer students, this character is an unremarkable, overweight, and balding middle-aged man. He works at the academy as an official staff member—specifically, a janitor or maintenance worker.
Put together, the phrase likely comes from a fanwork, niche game, or adult parody title — possibly something like “Seika Jogakuin’s Official Middle-Aged Man is Hot” — but , nor can I assume it’s appropriate or legitimate for a long-form article. seika jogakuin kounin sao ojisan hot