Marchosias is a Crimson Lord, a powerful being from the Crimson Realm, who is contracted to the Flame Haze Margery Daw. His true name is Claw and Fangs of Violation, and his flame is an ultramarine blue. He does not possess a physical body of his own in the human world; instead, his will is expressed through a divine vessel called the Grimoire, which takes the form of a large, ornate book that Margery carries. In this book form, he speaks directly to her and those around her.

In personality, Marchosias is loud, brash, and irreverent. He speaks without restraint, constantly making rude and teasing remarks, especially toward Margery. His comments frequently provoke her to punch him—book and all—across the room, earning him the nickname Baka-Marco from her. Despite this rough dynamic, he genuinely cares for Margery, not as a friend in the conventional sense but as a loyal companion and battle partner. He is a battle-loving Crimson Lord; his motivation for being involved in the Flame Haze’s fight stems largely from his own enjoyment of combat and the thrill of conflict, rather than a sense of duty or morality.

Within the story, Marchosias serves primarily as Margery’s power source and support. He provides her with her ultramarine flame and enables her to use powerful spells, often speaking out loud to assist in chanting or to offer sarcastic commentary during fights. He also acts as a means of transportation, as Margery can ride on the Grimoire when it expands. Additionally, he helps cure her hangovers, a recurring role given her heavy drinking habits. His relationship with Margery is central: they bicker constantly, but he remains fiercely protective of her in battle, and she relies on his strength.

Marchosias does not undergo significant personal development over the course of the series; his role and personality remain consistent. In one notable instance, when Margery loses control of her powers after being wounded, she unconsciously materializes a giant Toga in the shape of Marchosias’s true form into the real world. This form is that of a gigantic wolf, massive and fearsome, revealing his genuine nature as a powerful Crimson Lord. His main abilities revolve around lending his power to Margery, augmenting her spells and combat capabilities, and manifesting his wolf-like true form under extreme circumstances. Through his constant presence in the Grimoire, Marchosias remains an enduring, if often chaotic, fixture in Margery Daw’s life and in the larger conflict between Flame Haze and Crimson Denizens.