Cadis Etrama di Raizel, the "Noblesse" also known as "Rai," is enrolled in Ye Ran High School by his servant Frankenstein to remain hidden from the Union, a mysterious organization seeking Rai's life. Rai begins his life as a student, acquainting himself with his classmates and the daily routines of humans. However, his new existence is far from tranquil, and Rai is soon compelled to rescue his new friends from the Union, which has abducted them. Meanwhile, M-21—a Union agent who went rogue during Rai's rescue operation—joins the Ye Ran High School security staff following a proposal by the school's director, who is none other than Frankenstein himself. Outwardly, M-21 appears as a prim and proper employee, but in reality, he is bound by his former connections to the Union and the inevitable repercussions of betraying the organization. To further complicate matters, Nobles Regis K. Landegre and Seira J. Loyard enroll in the same school to investigate the Noblesse. While the Union conducts a manhunt for M-21 to extract clues regarding their missing agents, Rai is forced to conceal his identity while protecting everything he holds dear.