Motojirō Kajii is a volatile and eccentric figure whose personality mirrors the unpredictability of his lemon bombs. He is easily excitable, often speaking in a peculiar “code” centered on his fascination with the universe and science. For instance, he refers to the Port Mafia’s boss as the “Grand Marshal of Outer Space,” showcasing his unique perspective on the world. Kajii’s speech is typically loud and exclamatory, peppered with mocking remarks and self-aggrandizing declarations about his intelligence and scientific prowess.

Despite his erratic behavior, Kajii is a highly accomplished and enthusiastic scientist, deeply engrossed in the study of physics. He views science as the key to understanding and manipulating the world, integrating it into every aspect of his life and work. Kajii’s fascination with the concepts of life and death is particularly intense; he considers death a compelling phenomenon and views the lives he takes as necessary sacrifices for his “experiments.” This detachment from morality enables him to commit heinous acts without remorse, as he sees them as progress in his scientific endeavors. Kajii often ponders philosophical questions, such as the inevitability of death and its relationship with higher powers like God, which further drives his experiments.

As a member of the Port Mafia, Kajii is a committed and ruthless terrorist. His reputation as an explosives expert precedes him, making him one of the few mafiosi publicly known—a distinction he takes pride in. Kajii thrives in chaos, using his bombs and scientific knowledge to conduct ambushes and strategic attacks. He derives pleasure from mocking his opponents’ perceived inferiority, both in strength and intellect, while reveling in the destruction he causes.

However, Kajii’s confidence is not unshakable. When the tables turn against him, he is quick to cower and exhibit fear, revealing his lack of physical combat prowess. This tendency was particularly evident in his encounters with Akiko Yosano, whose defiance of death unsettled him deeply. Despite this, Kajii is cunning enough to use his apparent fear as a tactical advantage, as demonstrated when he pretended to fear Margaret Mitchell and Nathaniel Hawthorne to lower their guard.

At his core, Kajii views the world as dull and finds solace in his destructive creations, which he sees as the ultimate antidote to tedium. His lemon bombs, praised for their “perfect geometry,” symbolize his desire to dismantle the mundane world. For Kajii, the Port Mafia offers an outlet for his boundless creativity and scientific curiosity, granting him a space to pursue his chaotic “experiments” without restraint.

Motojirō Kajii is a tall, slim man with short brown hair, styled with evenly cut bangs across his forehead. His most distinctive facial feature is his purple-tinted goggles, which obscure his eyes and emphasize his eccentric appearance.

Kajii’s attire reflects his unconventional personality and obsession with science. He wears a tattered white lab coat with frayed sleeves and hem, giving him a disheveled and chaotic look. Beneath the coat, he sports a white button-down shirt cinched at the waist with a loose, brown belt-like accessory. His lab coat is adorned with several pins, each contributing to his quirky style. On the left side are two pins: a slightly larger yellow pin with a face and a smaller black pin with a red “X.” On the right side is an orange pin featuring an exclamation point, accompanied by metallic pins beneath it.

He pairs this with worn, frayed blue pants and a green scarf that adds a pop of color to his ensemble. Completing his look, Kajii wears traditional geta sandals, further highlighting his eccentric and unorthodox sense of style. His overall appearance perfectly encapsulates his chaotic, explosive personality and his role as an unpredictable scientist and terrorist.

Motojirō Kajii’s past remains largely shrouded in mystery. However, he is infamous for being one of the few publicly recognized members of the Port Mafia due to his notoriety as a terrorist. His most infamous act is the Maruzen Building Bombing, an incident that resulted in the deaths of 28 citizens and cemented his reputation as a ruthless and dangerous criminal.

In addition to his activities as a mafioso, Kajii is a lifelong student of physics and a self-proclaimed scholar. His deep fascination with science, particularly physics, heavily influences his actions, experiments, and worldview. While much about his early life remains undisclosed, it is clear that his intellect and scientific pursuits play a significant role in his character and his association with the Port Mafia.

Motojirō Kajii’s ability, Lemonade (檸レ檬モ爆ネー弾ド, Remonēdo), grants him immunity to the effects of any lemon-shaped bombs, including those he personally crafts. These bombs, a signature of his scientific and explosive expertise, are highly destructive and strategically deployed in his “experiments” and battles. While the specifics of how this immunity functions remain unexplained, it allows Kajii to wield his creations recklessly without fear of self-harm, giving him a significant advantage in combat scenarios.

Motojirō Kajii possesses a unique skill set centered around his passion for science and experimentation. As a self-proclaimed scholar of physics, Kajii applies his extensive scientific knowledge to create devastating explosives, particularly his signature lemon bombs. His fascination with the intersection of science and destruction fuels his relentless experiments and innovative approaches to weaponry. In addition to his expertise in physics, Kajii demonstrates a surprising understanding of human physiology, including specific conditions such as lactic acidosis. He is also well-versed in the precise details of human brain activity, such as how long consciousness persists after severe blood loss. This medical knowledge adds a morbid layer to his experiments, enabling him to explore the boundaries of life and death with unsettling precision.

The name Motojirō (基次郎) is composed of the kanji 基 (moto), meaning “foundation” or “basis,” 次 (ji), meaning “next” or “following,” and 郎 (rō), meaning “son” or “man.” Together, the name can be interpreted as “the foundational next son” or “a man who builds upon a foundation.”

The surname Kajii (梶井) combines 梶 (kaji), meaning “sculling oar,” symbolizing control or steering, and 井 (i), meaning “well,” often associated with water and sustenance. This surname could be understood as “the oar of the well,” possibly symbolizing guidance or resourcefulness.