Diogenes first appears in the anime as an eccentric Athenian hermit, easily recognized by his unkempt appearance and his unconventional choice of residence, a large ceramic tub in the public marketplace. His small stature and unusual features immediately mark him as an outsider, a role he seems to embrace. His way of speaking is notable for its distinct, inverted sentence structure, which adds to his cryptic and enigmatic aura. While his outward behavior and slovenly appearance initially suggest madness, this surface impression is a deliberate veil that conceals a profound connection to cosmic truths and a sharp, calculating philosophical mind.

Diogenes is driven by a deep-seated cynicism toward societal norms, power, and abstract knowledge. He lives in a state of extreme poverty by choice, appearing completely disengaged from the political and social ambitions that drive most other characters. This apparent detachment is, however, a tool rather than an escape. His core motivation is not to withdraw from the world but to influence it from an unexpected angle, using his outsider status to deliver truths that a conventional advisor could not. He dismisses the value of accumulated wisdom, as shown when he casually discards the Platohedron, a device containing universal knowledge that the revered Aristotle seeks. Diogenes values lived experience and the raw, chaotic force of passion over reason, believing passion to be the universe’s fundamental force. This philosophy positions him as a direct counterpoint to Aristotle's worldview.

Diogenes plays a pivotal role as an eccentric mentor and a philosophical catalyst for Alexander the Great. His most famous act in the story reenacts a legendary historical encounter. When the newly crowned Alexander, basking in his power, approaches Diogenes and grandly offers him any boon he desires, Diogenes responds by asking the king to move aside because he is blocking the sunlight. This seemingly impertinent request, however, is a masterful piece of political manipulation. By interpreting his request for sunlight as a claim to the prosperity of Athens, metaphorically embodied by the sun's warmth, Diogenes tricks Alexander into claiming Athens as Macedonian territory rather than sacking and plundering it. Through this linguistic precision, the mad hermit single-handedly prevents the destruction of a major city. Beyond this event, Diogenes acts as an interpreter of cosmic prophecy. He is acutely aware of Alexander's destiny to destroy the world. Later in the narrative, during Alexander’s final confrontation, Diogenes recontextualizes this prophecy, suggesting that destruction is not an end but a necessary precursor to rebirth and renewal.

His key relationships are defined by his intellectual opposition to authority figures. He stands in stark contrast to Aristotle, viewing the philosopher’s reliance on reason and accumulated knowledge as misguided. His most significant relationship, however, is with Alexander. Diogenes acts as a mirror to the conqueror, humbling him with a simple request and guiding him toward a deeper, more metaphysical understanding of his own path. He does not seek to be a friend or general to Alexander but rather a living embodiment of a truth that ambition and power must eventually confront. Diogenes shows little development in the traditional sense, remaining a static, almost elemental figure of wisdom. His significance in the story, however, deepens as his initial act of apparent madness is later revealed to be part of a greater cosmic awareness. His development is not in his own personality but in the unfolding revelation of his true nature as a mediator between the mundane world and prophetic destiny, a role that becomes clear when he helps Alexander reinterpret his grim fate not as final annihilation but as a transformative force.

Diogenes’ notable abilities are not physical but intellectual and metaphysical. His primary power is his penetrating insight, which allows him to see past illusions and grasp the true underlying nature of events and prophecies. He possesses a remarkable ability to manipulate language with extreme precision, turning a simple request into a binding political contract that saves Athens. Furthermore, he demonstrates a profound, almost supernatural connection to the cosmic truths of his world, understanding prophecies of destruction and rebirth that elude others. His ability to remain unmoved by the trappings of power is itself a form of strength, granting him a unique freedom to speak and act without fear or ambition.