Kagerō Usui occupies the role of class president for class 2-He, yet his position remains largely overlooked due to his defining attribute: an exceptionally faint presence. This near-total invisibility renders him effectively imperceptible to classmates and others unless his bald spot becomes uncovered. His name stems from the Japanese phrase "kage ga usui," signifying "overshadowed" or "faint presence," a direct nod to this condition. The "usui" element further references his thinning hairline and male pattern baldness.

He consistently appears with glasses and black hair that progressively thins across appearances. Typically, he combs his hair to mask his bald spot, but when this covering slips and reveals the spot, it momentarily grants him visibility and acknowledgment from others. This physical characteristic acts as the sole method through which he gains recognition.

Personality-wise, he exhibits self-consciousness about his hair loss, prompting efforts to conceal it. He displays perverted inclinations, frequently leering at female students like Kaere Kimura, though these actions escape notice due to his invisibility. He nurtures a specific romantic interest in Kobushi Abiru. An element of emotional masochism surfaces when he actively solicits additional insults from Chie Arai during her critiques of his appearance.

His core traits—extreme imperceptibility and reliance on his bald spot for visibility—persist without notable evolution throughout the series, seasons, or OVAs. He remains a consistent background figure whose fleeting moments of visibility arise exclusively from his bald spot's exposure.