Keisuke Sudō holds a supervisory position in a professional workplace, where his strict management style and high expectations earn him the nickname "demon boss." This professional rigor contrasts with his personal conduct during an off-duty encounter with intoxicated subordinate Saki Watase, whom he assists home. He discovers Saki possesses numerous XL-sized condoms through a product testing assignment and reveals his own physical compatibility with such products, sparking a romantic relationship.

Despite his characteristically serious approach to responsibilities, Keisuke demonstrates kindness. His dedication extends to meticulous product evaluation when participating in Saki's testing assignment. He exhibits notable possessiveness toward Saki. Their romance encounters complications with the arrival of Riku Narita, who develops interest in Saki and creates a competitive dynamic. Throughout these personal developments, Keisuke maintains consistent professional competence. His defined traits—strictness, dedication, unexpected charm, and physical possessiveness—remain unaltered.