From the Manufacturer

At age 14, Mizaru lost his sight due to a witch's curse. His story might have ended there except that he refused to become bitter. He, instead, focused his anger into overcoming the setbacks his injury initially posed. Honing his senses until he could navigate trails by the sway and sound of his scabbard, identify others by scent, and track any movement by the slightest noise, Mizaru eventually became Captain of the Yamazaru' s famed scouts.