Ōetsu Nimaiya holds the position of Third Officer within the Royal Guard (Zero Division) and bears the title "Divine General of the West." His creation of the Zanpakutō earned him recognition from the Soul King and secured his promotion to the Royal Guard. This foundational achievement established his identity as the "God of the Sword." He possesses dark skin and thick black hair, shaved and dyed green on the sides. His attire modifies the standard Shinigami shihakushō, featuring a green undergarment and a shortened hakama that exposes his lower legs. He wears a white sleeveless puffer jacket bearing the Royal Guard emblem and the captain's haori pattern, complemented by gold-framed blue-lens sunglasses and green-and-gold trimmed slippers. His personality blends unpredictability with energetic and grandiose mannerisms, often mixing Japanese and English in his speech. This lively demeanor persists during combat, where he engages in casual banter while delivering lethal blows. He demonstrates pragmatic ruthlessness, exemplified by slitting his own throat to circumvent Askin Nakk Le Vaar's The Deathdealing ability, immediately coordinating a blood transfusion with fellow Royal Guard member Tenjirō Kirinji. Functionally, he forges every Asauchi—the blank Zanpakutō templates distributed to Shinigami recruits. These entities imprint with a wielder's soul essence over time, developing unique characteristics and names. He maintains awareness of every Zanpakutō's location and remains the sole individual capable of reforging broken blades. His palace, the Phoenix Palace, serves as the forge for this work. During the Thousand-Year Blood War arc, he arrives in Soul Society following Captain-Commander Yamamoto's death, later transporting Ichigo Kurosaki and injured allies to the Soul King Palace. His training regimen for Ichigo and Renji Abarai involves shattering their existing Zanpakutō and subjecting them to a trial against hostile Asauchi within a specialized hut. After three days, he declares Ichigo a "failure," citing the Asauchi's rejection due to Ichigo's unconventional origins and lack of a true Asauchi base—Ichigo's Zanpakutō originated from White, a Hollow crafted by Sōsuke Aizen from a Shinigami soul, functionally similar to an Asauchi. Nimaiya later reverses his decision, allowing Ichigo to select an Asauchi. During the reforging process, he reveals critical truths: Zangetsu's manifestation represents Ichigo's latent Quincy powers resembling a younger Yhwach, while his inner Hollow constitutes his actual Zanpakutō spirit. He supervises as Ichigo merges these elements, resulting in twin Zangetsu blades. In combat against Yhwach's Schutzstaffel, he wields his Zanpakutō, Sayafushi. This blade, suspended in jelly when unused, produces a distinctive zooming sound during swings. Its flaw lies in excessive perfection—extreme sharpness and smoothness prevent sheathing and cause substances like blood to slide off its surface; its guard lacks ornamentation, reflecting this minimalist flaw. Using Sayafushi, he delivers swift, lethal strikes to Gerard Valkyrie, Lille Barro, Pernida Parnkgjas, and Askin Nakk Le Vaar. His combat style prioritizes evasion, precision, and adaptability, though he ultimately sustains injuries against the revived Schutzstaffel enhanced by Yhwach's Auswählen.