Marcus Lithos is a young man who becomes the wielder of the Azoth Sword, a legendary cursed weapon said to house the demon Beelzebub. He originally suffered a paralyzing accident, and his search for a cure led him to the Azoth Sword, which restored his mobility but bound him to its dark influence. He presents himself as a calm, affluent aristocrat, but beneath this composed exterior he hides an unstable core, deeply shaken by past trauma and betrayal. His persistent yearning for genuine connection drives him to simulate a family life, blurring the boundary between reality and fantasy as he tries to fill an emotional void.

Within the story, Marcus serves as a supporting character aligned with the Shoshidai, an organization dedicated to collecting and containing cursed weapons. He operates as a Chrysalis, a human who wields a cursed weapon while struggling to retain his humanity. He is paired with the Shoshidai agent Miki on several missions, and later becomes involved in a romantic relationship with a woman named Aya. His development is marked by a gradual psychological unraveling: despite his outward success and restored physical abilities, his fragile mental state leads him to construct an idealized family life, illustrating how the combination of trauma and the corrupting influence of the Azoth Sword erodes his sense of reality.

Notable abilities stem from his bond with the Azoth Sword, granting him enhanced combat capabilities and supernatural powers derived from the weapon's demonic nature. However, his dependence on the sword also makes him vulnerable to its corrupting influence, threatening to consume his remaining humanity. Marcus Lithos is an anime‑original character whose tragic arc explores themes of loss, identity, and the desperate human need for belonging.