Muramasa

Green, keen eyes and a two-toned mane define Kōga's younger self: black hair falling past the shoulders behind a sweeping red ponytail, worn with a fringe over the right cheek. As a serving officer he dressed his black uniform up with noble touches, chief among them the white kenseikan clasped at the left of his scalp, plus a red scarf, a lavender waist-tie, and a beaded pendant. In renouncing the clan, he tore that headpiece away for good.

What the long imprisonment returned was a shell of him, wasted thin from starvation. Restraints from his cell clung on, shackles at the wrists and a mask whose lower half had been cut so only the nose bridge stayed. Robes ripped to expose his chest, he kept just the scarf and necklace from before.

Confidence sat at Kōga's core from the start, a headstrong drive to charge in and settle any fight, tempered by real devotion to peace and a willingness to die for it. He sought his Zanpakutō spirit's advice often and longed, quietly, for his father-in-law Ginrei Kuchiki to acknowledge victories that kept going unpraised. When rival officers framed him for murder to steal his glory, that unmet need curdled into something poisonous.

Prison and a punishment he blamed on Ginrei's supposed doubt broke his grip on reason. He killed his framers only to feel empty, then talked himself into believing everyone alive hated and envied him. Discarding the Kuchiki name, he turned his blade on innocents to spread hopelessness across Soul Society, embracing despair as fuel and preaching that raw power alone dictates justice. To Kōga a sword was a mere implement beneath its master, a stance that led him to abuse and finally destroy the very spirit that had stood by him.

Kōga's reiryoku ran deep enough that Ginrei admitted it eclipsed his own, and Muramasa judged it far from its limit; a single wave of his indigo pressure could scatter Ichigo Kurosaki and Rukia Kuchiki even centuries later. From it he drew two signature arts he said he had gifted to his sword: threads of spirit energy that shackle a target by trapping their shadow rather than their reflection, and full-sensory illusions that conjure phantom strikes, doubles, and false distances, usable only if a foe leaves their heart unguarded.

A polished swordsman, Shunpo master, and Kidō adept, he chained unincanted spells against Byakuya Kuchiki and, after breaking his own katana, fought on with the four sealing halberds as improvised weapons. His Zanpakutō Muramasa answered the release word 'Whisper' and made other blades betray their owners, while its Bankai, Mukōjōchū Muramasa, brought the spirit fully into the physical world. His deepening insanity severed that partnership by degrees, until his calls to the sword met only silence.