Asakusa Demon

Until that night, the man drew no attention: medium build, light skin, cropped black hair, and brown eyes, dressed in a greenish-gray haori over an indigo kimono with a gray hakama. As he walked a packed evening lane beside his spouse, Muzan slipped close and raked his neck with sharpened nails before vanishing into the crowd. The tainted blood worked inward, his irises bled into red, his pupils narrowed inside a faint pale glow, fangs formed, and he convulsed into a feral creature.

Only Tanjiro saw the assault. He tore the changed husband away from the woman, gagged him with a length of cloth, and kept him pinned. Bystanders and arriving officers read the chaos as a drunken brawl, but Tamayo appeared, hid the young slayer from view with her own illusion, and carried the couple to her residence, treating the wife and locking the demon below. Later, using blood Tanjiro had collected, she succeeded in an early reversal that returned the man's mind and human shape, severing Muzan's command over him. His significance resurfaced in the closing campaign, when Tamayo revealed that the thorny growths trapping Muzan at a decisive instant sprang from this very man's power.

Freshly turned, he barely qualified as a threat, dangerous only to his shaken wife and the frightened onlookers, and a single rookie subdued him without difficulty. Buried inside him, though, lay something far from trivial. The technique, Flesh Seeds, produced small nodes that erupted into massive thorns, skewering a target and threading deeper into the flesh. When deployed against Muzan, these spikes surfaced all at once and held the demon king fixed in place, granting Tamayo the narrow opening required to deliver her drug.