Crimson is a central figure and one of the protagonist characters in the narrative. The true identity of this androgynous figure is the former Dragon King of the Winged Bloodline, holding the rank of number one among the six Dragon Kings before their fall from power. Crimson rebelled against the Dragon God, an act of high treason that led to being stripped of the title and most of their draconic power. Exiled and hunted by their own kind, Crimson now operates from the shadows with a singular, all-consuming objective: the complete eradication of every dragon in existence, a goal from which Crimson themself is not exempt.

The character's personality is a complex blend of cold arrogance and pragmatic ruthlessness. Having once stood at the pinnacle of dragon society, Crimson retains a superior and overconfident demeanor when interacting with others. However, this pride is secondary to an almost obsessive focus on results. Crimson is a master strategist and a cold-blooded utilitarian, evaluating every person and situation solely based on their usefulness in the war against dragons. The lives of allies, subordinates, or innocent bystanders are considered expendable resources to be consumed for the sake of achieving a strategic advantage. This heartless pragmatism puts Crimson in direct opposition to the idealistic values of their primary partner, Ragna, who fights to protect the innocent. Despite these clashes, Crimson is not a fool driven solely by ego; when the situation is unfavorable, they will relentlessly work to regain the initiative through cunning and deception rather than blind pride. Interestingly, this composed and manipulative facade can shatter spectacularly when plans go awry, revealing a surprisingly childish and petulant side prone to dramatic outbursts when frustrated.

Crimson's primary role in the story is that of a hidden puppeteer and a reluctant mentor to the protagonist, Ragna. After their failed future rebellion, Crimson orchestrated a plan to send Ragna's power and memories back in time, creating an unprecedented weapon against the dragons. In the present, Crimson serves as Ragna's guide, strategist, and often his most antagonistic ally, constantly pushing him toward efficiency and ruthlessness. The relationship between the two is the story's core dynamic; it is purely transactional from Crimson's perspective, built on mutual necessity rather than trust or friendship. Crimson views Ragna as the most valuable tool for dragon slaying, while Ragna and his allies in the Silver Corps see Crimson as a necessary evil or a "dark mass of death" rather than a comrade. Despite this friction, Crimson maintains a few loyal subordinates, such as the golem, chimera, and slime, who serve their master's will without question.

A former Dragon King, Crimson possesses a vast arsenal of abilities, though most have been drastically reduced after sealing away their heart. This act of sealing is what grants Crimson a unique form of immortality; by storing their heart in another dimension, physical death is merely an inconvenience, as a new body will manifest elsewhere. However, this immortality comes at the cost of their original power. While in this sealed state, Crimson cannot use the full might of a Dragon King but also lacks a dragon's classic weakness to sunlight. Even in this weakened form, Crimson is a formidable magic user, proficient in hypnosis, mental manipulation, and advanced magical rituals. Their true specialty is resourcefulness and preparation, utilizing a hidden dimension known as the Globe, which acts as a teleportation hub and houses a vast arsenal of advanced weaponry. In desperate situations, Crimson can retrieve their heart to regain a fraction of their former power—roughly ten percent. In this state, they recover the ability to manipulate space and time, though they cannot yet match the might of a reigning Dragon King like Ultimatia, and they regain their species' vulnerability to sunlight.