Hades, known in the human vessel as Alone, is a central figure in the 18th century Holy War, serving as the earthly incarnation of the god of the Underworld. Alone is introduced as a young and gentle teenager of Italian origin, raised in an orphanage in a remote Italian village alongside his best friend, Tenma, who is destined to become the Pegasus Saint, and his younger sister, Sasha, who is the reincarnation of the goddess Athena. Before his dark destiny unfolds, he is characterized by a profoundly pure and kind heart, a quality that directly leads to him being chosen as the mortal vessel for Hades, as the god requires the most unsullied soul for his reincarnation. He is deeply passionate about painting and harbors a strong aversion to violence, once even scolding Tenma for fighting back against bullies.

Initially, Alone rejects his fate as the god of the dead. However, his personality undergoes a drastic transformation after he discovers that everything he paints dies. Manipulated by the twin gods Hypnos and Thanatos, who appear to him as a priest and his assistant, he is led to believe that death is the ultimate and only true form of salvation for humanity. Convinced that he can spare the world from the endless cycles of pain, war, and poverty, Alone accepts the power of Hades. This awakening is symbolized by a shift in his appearance; his hair, initially blonde, turns black as he embraces the dark power. His core motivation becomes the completion of the "Lost Canvas," a massive, celestial painting of the Earth from space. According to his plan, once the final stroke is applied and the Stellar Clock visible in the night sky completes its cycle, the entire mortal world will perish and thus be "saved" from suffering.

Throughout the narrative, Alone occupies a complex and ambiguous role. While worshipped as the emperor of the 108 Specters and the leader of Hades's army, he often acts independently of his divine servants. In a significant twist, he later reveals that he was never truly possessed or controlled by the will of Hades; rather, he has been using the god's immense power to pursue his own misguided philosophy of universal salvation. His key relationships are defined by tragedy. His love for his sister Sasha and his best friend Tenma is twisted into a desire to "save" them through death, making him their greatest enemy in the Holy War. He is served loyally by the Specter Pandora, who considers him a bird trapped in a cage, and the powerful Benu Kagaho, but he ultimately views even his followers as part of the flawed world he seeks to end.

Alone's development arc moves from innocence to despair and then to a terrifyingly resolute, messianic conviction. He genuinely suffers from the power he wields, feeling the loss of those he accidentally kills, but steels himself to complete his mission. In the final confrontation, his original gentle personality resurfaces, and he pleads with Tenma to destroy his body to prevent the complete resurrection of the true god Hades. When the god's will finally does overwhelm him, his appearance shifts entirely to match Hades's true divine form, representing the climax of the internal struggle between the human and the god. As a painter wielding the power of a god, his most notable ability is the lethal power of his art. He does not fight with traditional weapons but with a divine paintbrush; anything he paints dies or is destroyed, including living beings and even Saints in their armor. He can use this power to create destructive barriers, kill opponents from a distance, and construct the reality-warping Lost Canvas itself. Additionally, as Hades's vessel, he possesses immense physical strength, capable of easily overpowering Gold Saints like Sagittarius Sisyphus and surviving attacks that would annihilate normal beings.