Motojirō Kajii operates as a Port Mafia terrorist specializing in bomb-making, recognized publicly for his destructive acts. His distinct attire includes purple-tinted goggles, a frayed white lab coat pinned with a yellow face and black "X," a green scarf, and geta sandals. He stands 180 cm tall with a slim 63 kg frame, short brown hair trimmed evenly above his forehead. Kajii's eccentricity manifests as a scientific obsession with death and the cosmos. He addresses the Port Mafia boss as "Grand Marshal of Outer Space" and frames bombings as experiments against boredom, expressing fascination with biological decay like lactic acidosis without remorse. His interests cover lemons, opera, wine, and science; he avoids crowded streets and jazz. His ability, **Lemonade**, immunizes him against explosions from his handcrafted lemon-shaped bombs. The ability solely provides protection, not bomb creation. These devices incorporate undetectable elements, making their design coveted in the underworld. He deploys them in ambushes and surprise assaults. Kajii is a wanted terrorist accountable for 28 civilian deaths in the Maruzen Building Bombing. A lifelong physics scholar, his early history remains obscure. During a mission to capture Atsushi Nakajima, he bombed a subway train with Kyōka Izumi, killing civilians. He confronted Akiko Yosano, theorizing on death until her regenerative ability defeated him. In a Guild conflict, he faked surrender to Nathaniel Hawthorne and Margaret Mitchell, then destroyed their ship with hidden bombs, eliminating Guild operatives and incapacitating Mitchell. When the Armed Detective Agency raided Port Mafia headquarters, he executed **Lemon Flower Path**—strapping bombs to his body and charging enemies while detonating them to stall their advance. Despite his destructive prowess, Kajii retreats when physically overpowered, as demonstrated against Yosano and during his capture by the Guild. The character references author Motojirō Kajii (1901–1932), drawing from his story "Lemon" where a tuberculosis patient imagines the fruit as a bomb. This inspiration informs Kajii's lemon bombs and theatrical mortality themes.