Nagi manifests as a divine serpent beast in human guise, initially appearing as a half-serpent man residing within an ancient Asian-inspired palace located in an alternate world devoid of women. His fundamental purpose as a divine beast demands transformation into a dragon, achievable solely through ritualistic intercourse with a summoned human partner designated as his Miko, or shrine priestess. This union is essential for his ascension to a higher state.

He identifies Kotone Aizuhara, a deceased human male summoned from another world, as his destined Miko. Nagi directly informs Kotone of their necessary physical relationship, presenting it as an unavoidable destiny intrinsically tied to his divine nature and evolutionary path. His initial demeanor establishes him as resolute and forthright regarding this imperative.

Over time, Nagi's connection with Kotone evolves beyond the initial ritual requirement. Despite Kotone's attempts to evade emotional entanglement by invoking his knowledge of boys-love tropes, Nagi's persistent pursuit and the progression of their interactions indicate a shift toward mutual emotional connection. This development coincides with his ongoing physical transformation journey toward dragonhood, though the specific stages of this evolution remain undefined.

His origins, life prior to summoning Kotone, and experiences outside his interactions with the summoned human and the immediate depicted world remain unrecorded. His character is centrally defined by his role as a divine beast seeking transcendence through the bond forged with his Miko.